553.464909788 
G293m 


THE 

MAIN  TUNGSTEN  AREA 

OF 

BOULDER  COUNTY 
COLORADO 


Reprinted  with  Additions  from  the 

First  Report  of  the 
Colorado  Geological  Survey 


Boulder,  Colorado 
1916 


THE 

MAIN  TUNGSTEN  AREA 


OF 

BOULDER  COUNTY 
COLORADO 


Reprinted  with  Additions  from  the 

First  Report  of  the 
Colorado  Geological  Survey 


By 

R.  D.  GEORGE 

With  Notes  on  the  Intrusive  Rocks  by 

R.  D.  CRAWFORD 


Boulder,  Colorado 
1916 


,ri  a ewtofi 


CONTENTS. 


INTRODUCTORY  . — IS 

HISTORICAL  — — — ^ — — - IS 

ACKNOWLEDGMENTS  — — ------ 14 

LOCATION - - 14 

TOPOGRAPHY  — — — 15 

CLIMATE  AND  VEGETATION — 15 

CHAPTER  I.— GENERAL  GEOLOGY. 

INTRODUCTION  16 

GRANITE  AND  GNEISSOID  GRANITE 17 

Mineral  Composition  17 

Weathering  18 

Origin  : 18 

gneiss  18 

Structural  Features 19 

Origin  19 

fine  grained  granite 20 

pegmatite  20 

Mrural  Composition  _ 22 

xxntkUSIVE  23 

ANDESITES  24 

Hornblende  Andesite 24 

Glassy  Hornblende  Andesite 24 

Mica  Andesite 25 

Pyroxene  Andesite 25 

felsite  26 

DACITE  27 

latite  : 27 

LATITE  PORPHYRY  28 

Soda  Rhyolite  30 

DIABASE  30 

LAMPROPHYRE  31 

BASALTS  AND  BASALT  PORPHYRIES 31 

Basalt  32 

Hornblende  Basalt 32 

Basalt  Porphyry 33 

PYROXENITE  33 


348182 


8 CONTENTS. 


CHAPTER  I.— GENERAL  GEOLOGY.— Continued. 

LIMBURGITE  34 

SURFACE  DEPOSITS  34 

Glacial  34 

Alluvial  35 

CHAPTER  II.— ECONOMIC  GEOLOGY. 

TUNGSTEN  MINERALS  37 

Hubnerite  37 

Wolframite  v 37 

Scheelite  38 

Ferberite  41 

Analyses  of  Ferberite  frcm  Nederland-Beaver  Creek 

Area 42 

Analyses  (Partial)  of  Nederland  Ores 42 

Analyses  of  Ores  of  Northeastern  Area 43 

Analyses  of  Tungsten  Ores  from  Other  Parts  of  Colo- 
rado  43 

Minerals  Resembling  the  Dark  Tungsten  Ores 44 

Other  Tungsten  Minerals 45 

TESTS  FOR  TUNGSTEN 45 

OCCURRENCE  OF  TUNGSTEN  MINERALS 46 

Scheelite  47 

Wolframite  and  Hubnerite 48 

Ferberite  49 

TUNGSTEN  LOCALITIES  IN  THE  UNITED  STATES 49 

Washington  51 

Oregon  51 

California  51 

Arizona  51 

Nevada  52 

Utah  52 

Idaho  52 

Montana  52 

Wyoming  52 

Colorado  53 

New  Mexico 53 

Texas  * 53 

South  Dakota  53 

Missouri  53 

North  Carolina 53 

Virginia  53 


CONTENTS. 


9 


CHAPTER  II.— ECONOMIC  GEOLOGY.— Continued. 

TUNGSTEN  LOCALITIES  IN  THE  UNITED  STATES. — Continued. 

Connecticut  54 

Maine  54 

IMPORTANT  TUNGSTEN  DEPOSITS  IN  THE  UNITED  STATES 

(OMITTING  BOULDER  COUNTY)  54 

Arizona,  Near  Dragoon,  Cochise  County,  and  Gigas,  Near 

Arivaca,  Santa  Cruz  County 54 

California,  the  Randsburg  District i 54 

Nevada,  Tungsten  Mining  District,  South  of  Ely 54 

South  Dakota,  Black  Hills 55 

Colorado,  San  Juan 55 

FOREIGN  TUNGSTEN  DEPOSITS 56 

Australasia  56 

Europe  57 

Africa  58 

Asia  58 

South  America  58 

Canada  59 

• ORE  BODIES,  BOULDER  COUNTY 61 

Country  Rock  of  the  Deposits 61 

Trend  of  Veins 62 

Vein  Structure  and  Vein  Filling 63 

Outline  of  Vein  Development 63 

The  Ores  67 

The  Gangue 75 

Other  Vein  Minerals 75 

MINING 76 

CONCENTRATION  76 

Mills  76 

Difficulties  79 

The  Boulder  County  Mill 82 

The  Claras  dor  f Mill 83 

The  Boyd  Mill 83 

Mill  Practice  of  Atolia  Mining  Company,  California 84 

Australian  Milling  84 

Cornish  Tungsten  Ore  Dressing 84 

Sale  of  Ore  and  Concentrates 85 

EXTENSION  OF  THE  AREA 85 

Future  of  the  District 85 

PRODUCTION  86 


10  CONTENTS; 

CHAPTER  III.— TECHNOLOGY  AND  USES  OF  TUNGSTEN. 

THE  METAL  AND  ITS  METALLURGY 87 

The  Metal 87 

Metallurgy  87 

USES  OF  TUNGSTEN  AND  TUNGSTEN  COMPOUNDS 88 

Introduction  88 

Metallic  Tungsten — Tungsten  Lamps 89 

Tungstic  Oxide  : 90 

Tungstates  91 

ALLOYS  OF  TUNGSTEN 91 

Various  Alloys  91 

Iron  and  Steel  Alloys 92 

F err  o-Tungsten  * 92 

Tungsten  Steel  93 

Uses  of  Tungsten  Steel 94 

Manufacture  of  Tungsten  Steel 95 

BIBLIOGRAPHY  106 


CONTENTS. 


11 


CONTENTS  TO  SUPPLEMENTARY  REPORT. 


EXTENSION  OF  THE  AREA 96 

TUNGSTEN  IN  OTHER  COUNTRIES 96 

India  96 

Portugal 97 

Canada  97 

Japan  97 

THE  BOULDER  COUNTY  TUNGSTEN  MINERALS 97 

Ferberite  97 

Scheelite  97 

Hubnerite  98 

Tungstic  ochre,  tungstite 98 

THE  DARK  TUNGSTEN  MINERALS 98 

Ferberite  99 

Hubnerite  99 

Wolframite  99 

ASSOCIATED  MINERALS 99 

CONCENTRATION  99 

METALLURGY  100 

USES  OF  TUNGSTEN 101 

METALLIC  TUNGSTEN 102 

TUNGSTEN  STEEL 102 

THE  PHYSICAL  AND  CHEMICAL  PROPERTIES  OF  THE  METAL 103 

ALLOYS  104 

TUNGSTEN  PRODUCTION  ON  BASIS  OF  60%  W03 105 

ADDITIONAL  BIBLIOGRAPHY 112 


/ 


■ 


INTRODUCTORY. 


HISTORICAL. 

Hubnerite,  and  probably  wolframite  have  been  known  in  the 
San  Juan  for  over  twenty  years,  and  scheelite  was  long  ago  re- 
ported from  Chaffee  and  Summit  counties.  A number  of  mines  of 
the  San  Juan  have  produced  a few  tons  of  tungsten  concentrates, 
mainly  as  a by-product,  but  no  vigorous  development  of  the 
hubnerite  deposits  has  been  attempted.  In  1870  Sam  P.  Conger, 
the  veteran  prospector,  discovered  the  Cariboo  Mine  and  a few 
months  later  the  Boulder  County  Mine.  The  Cariboo  camp  be- 
came very  active,  and  both  miners  and  prospectors  soon  became 
familiar  with  the  heavy  dark  mineral  which  occurred  as  float  in 
the  district.  It  was  called  by  various  names,  such  as:  “heavy 
iron/'  “hematite,”  “black  iron,”  “barren  silver,”  and  others. 
Many  assays  were  made,  but  its  true  character  was  not  discovered 
until  Conger’s  partner,  W.  H.  Wanamaker,  returned  from  Ari- 
zona, where  he  had  seen  the  tungsten  ore  from  the  Dragoon 
Mountains.  They  kept  the  identity  of  the  ferberite  a secret,  and 
started  negotiations  to  secure  possession  by  lease  or  otherwise 
of  a part  of  the  Boulder  County  ranch  for  the  purpose  of  mining 
the  placer  tungsten  ore  and  developing  the  veins.  Conger  secured 
the  lease  in  August,  1900,  and  by  the  end  of  the  year  had  taken 
out  about  40  tons  of  high-grade  ore.  This  was  handled  by  the 
State  Ore  Sampling  Company,  Denver,  and  half  of  it  netted  abdut 
$1.60  per  unit.  The  other  half  was  sold  to  Mr.  Morris  Jones, 
representating  the  Great  Western  Exploration  and  Reduction 
Company,  at  $60.00  per  ton,  or  $1.00  per  unit.  Mr.  T.  S.  Walte- 
meyer  was  associated  with  Conger  and  Wanamaker,  and  concen- 
trated their  ore. 

For  1901  a production  of  65  tons,  running  65  per  cent,  tung- 
stic oxide,  is  reported.  This  was  sold  at  about  $2.25  per  unit.  In 
1902  the  market  was  extremely  dull  and  much  difficulty  was  ex- 
perienced in  selling  the  concentrates.  But  considerable  pros- 
pecting was  in  progress  and  some  development  was  done.  The 
year  1903  was  very  favorable  for  the  tungsten  producer,  and  rapid 
development  marked  the  history  of  the  Boulder  County  area. 
From  that  time  until  nearly  the  end  of  1907  development  was  rea- 
sonably steady.  But  the  financial  depression  put  a check  upon 


14 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


progress,  from  which  the  recovery  is  not  even  yet  complete.  Much 
exploratory  and  development  work  has  been  going  on  during  the 
last  few  months,  and  the  year  1909  promises  considerable 
activity. 

The  field  work  was  begun  in  the  summer  of  1907  and  com- 
pleted in  the  summer  of  1908, 

ACKNOWLEDGMENTS. 

The  writers  take  this  opportunity  of  thanking  all  the  owners, 
operators  and  managers  of  mines  and  mills  for  their  assistance, 
which  has  contributed  much  to  the  value  of  this  report.  They 
would  like  to  mention  a few  who  were  called  upon  more  freely 
than  were  the  others,  and  who  were  always  ready  to  assist : Mr. 
C.  F.  Lake,  Mr.  Morris  Jones,  Mr.  H.  F.  Watts,  Mr.  Wm.  Loach, 
Mr.  Henry  E.  Wood,  Mr.  V.  G.  Hills. 

The  greater  part  of  the  chemical  work  was  done  at  the  Uni- 
versity of  Colorado  under  the  direction  of  Dr.  J.  B.  Ekeley. 

It  would  be  impossible  to  acknowledge  in  the  text  of  this 
report  all  the  sources  from  which  facts  have  been  drawn.  The 
literature  of  tungsten  is  extremely  fragmentary  and  unsatisfac- 
tory, and  many,  perhaps  the  majority,  of  the  references  in  the 
bibliography  at  the  end  of  this  report  are  to  articles  ranging  in 
length  from  four  or  five  lines  to  a page.  Many  more  references 
could  have  been  added,  but  the  greater  number  would  have  been 
to  matter  outside  the  purpose  of  this  report. 

LOCATION. 

The  principal  part  of  the  tungsten  district  lies  in  the  south- 
eastern quarter  of  Boulder  County,  but  some  promising  discov- 
eries have  been  made  in  the  northern  part  of  Gilpin  county.  It 
is  covered  by  the  northern  six  miles  of  the  Black  Hawk,  the 
southern  two  miles  of  the  Boulder,  and  the  northeastern  corner 
of  the  Central  City  topographic  maps  of  the  U.  S.  Geological  Sur- 
vey. Another  small  area,  not  yet  producing,  lies  chiefly  east  of 
Ward  in  the  Boulder  quadrangle.  The  principal  places  in  the 
district  are  Nederland,  Cardinal,  Phoenixville,  Rollinsville,  Sugar- 
loaf  and  Magnolia.  The  Denver,  Boulder  and  Western,  formerly 
The  Colorado  and  Northwestern  railway  (operated  by  the  Colo- 
rado and  Southern)  runs  from  Boulder  into  the  tungsten  field, 
and  has  stations  at  Sugarloaf,  Tungsten  and  Cardinal.  The 
Denver,  Northwestern  & Pacific,  (The  Moffat  Road),  has  a 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


15 


station  at  Rollinsville.  A daily  stage  runs  from  Boulder  to 
Nederland,  eighteen  miles. 

TOPOGRAPHY. 

The  area  is  a part  of  a broad  eastward-sloping  upland  belt 
extending  from  the  ridges  of  upturned  sedimentary  rocks  at  the 
western  border  of  the  Great  Plains,  westward  to  the  steeper 
slopes  of  the  Front  Range.  This  belt  is  an  old  erosion  plain,  now 
deeply  dissected  by  a series  of  eastward  flowing  streams  and  their 
tributaries  occupying  canon-like  valleys  from  which  many  gulches 
cut  back  well  toward  the  divides.  The  principal  streams  of  the 
area  are  North  Boulder,  Middle  Boulder,  South  Boulder  and 
Beaver  Creeks.  A few  outstanding  points  such  as  Sugarloaf  and 
Bald  mountain,  and  those  near  Rollinsville,  are  erosion  remnants 
of  the  earlier  period  of  downcutting,  which  was  approaching 
base  level  before  the  post-Laramie  uplift,  which  increased  the 
vigor  of  the  streams  and  caused  them  to  cut  their  deep  narrow 
valleys  in  the  resistant  metamorphic  rocks. 

The  transition  from  the  western  border  of  the  plains  to  the 
eastern  border  of  the  upland  belt  is  abrupt.  Within  a mile  the 
difference  of  elevation  may  be  as  great  as  2,000  feet,  while  the 
average  elevation  of  the  upland  above  the  western  border  of  the 
plains  is  about  2,500  feet.  This  greater  elevation  is  due  to  two 
causes:  a.  differential  uplift  at  the  close  of  the  Cretaceous,  by 
which  the  foothills  and  mountain  area  was  raised  more  than  the 
plains  region,  and  b.  differential  erosion — the  more  rapid  lower- 
ing of  the  surface  of  the  plains  by  the  erosion  of  the  less  resistant 
sedimentary  rocks  of  the  plains. 

CLIMATE  AND  VEGETATION. 

The  climate  is  that  characteristic  of  the  foothills.  On  the 
eastern  border  the  annual  rainfall  (including  snow)  is  about  16 
inches,  while  that  of  the  western  border  is  somewhat  greater. 
Vegetation  is  nowhere  very  abundant,  though  dense  growths  of 
evergreens  cover  many  of  the  favorably  situated  slopes.  The 
timber  is  seldom  large. 


16 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


CHAPTER  I.— GENERAL  GEOLOGY. 


INTRODUCTION. 

The  area  is  wholly  within  the  pre-Cambrian  belt,  called, 
in  a broad  way,  the  Front  Range.  The  nearest  sedimentary 
rocks,  except  recent  stream  and  lake  deposits,  are  three  miles 
to  the  east.  The  most  important  rock  is  granite,  generally  more 
or  less  gneissoid.  Next  in  importance  is  a granitic  gneiss  fre- 
quently grading  into  quartz-mica-schist  and  mica  schist.  While 
the  areas  occupied  by  these  two  units  are,  in  a large  way,  well 
defined,  there  are  numerous  bodies  of  gneiss  within  the  granite, 
and  numerous  bodies  of  granite  within  the  gneiss.  In  a number 
of  places  there  is  no  well-defined  contact  line  between  the  two, 
but  a band  or  zone  in  which  the  two  rocks  are  mingled,  and  in 
which  there  is  frequently  a gradual  transition  from  one  type  to 
the  other. 

Cutting  the  gneissoid  granite  and  the  gneiss  are  granite  in- 
trusions in  the  form  of  dikes  and  irregular  bodies.  In  the 
western  and  northern  parts  are  many  dikes  ranging  in  composi- 
tion from  acidic  porphyries  to  latites,  andesites,  diabase  and 
basalt. 

The  two  main  types  of  country  rock  mentioned  above  are 
themselves  complex  bodies,  consisting,  in  each  case,  of  a pri- 
mary formation  and  many  intruded  rock  masses.  The  ratio 
of  the  intruded  rocks  to  the  primary  rocks  varies  from  place 
to  place,  but  for  the  whole  region  it  is  large.  The  intrusions 
vary  in  age,  and  consequently  in  the  degree  of  change  which 
they  have  undergone.  The  oldest,  having  passed  through  many 
of  the  metamorphic  processes  to  which  the  containing  forma- 
tion has  been  subjected,  bear  a very  close  resemblance  to  it, 
and,  in  places,  are  with  the  greatest  difficulty  distinguished 
from  it.  The  latest  intrusions,  on  the  other  hand,  probably 
date  from  the  last  great  mountain-making  disturbance,  and 
consequently  show  comparatively  slight  metamorphism.  Apart 
from  the  dike  rocks,  however,  there  is  but  little  strictly  non- 
metamorphic  rock  within  the  area.  The  beginnings  of  meta- 
morphism are  shown  in  the  development  of  an  indistinct  direc- 
tional structure,  and  in  the  partial  assembling  of  the  mica  into 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY, 


17 


bunches  and  ill-defined  planes.  These  alterations  of  the  intruded 
rock  are,  as  a rule,  much  more  pronounced  in  the  gneiss  than  in 
the  granite. 

THE  GRANITE  AND  THE  GNEISSOID  GRANITE. 

So  far  as  the  tungsten  district  is  concerned,  this  is  by  far 
the  most  important  rock,  both  in  area  occupied  and  in  its  rela- 
tion to  the  ores. 

Lithological  character:  Within  the  area  mapped  as  granite 
there  are  very  wide  lithological  variations.  From  the  pre- 
vailing type — a slightly  gneissoid  granite — there  are  transi- 
tions, on  the  one  hand,  to  a perfectly  massive  granite  showing 
no  evidence  of  directional  structure  or  segregation  of  the 
minerals,  and,  on  the  other  hand,  to  a rock  in  which  the 
segregation  of  the  mica,  in  particular,  is  very  pronounced,  and 
in  which  a directional  structure  is  very  noticeable.  In  certain 
parts  of  the  area  there  seems  to  have  been  a poorly  defined 
blocking  of  the  rock  in  immense  masses  bounded  by  pronounced 
jointing  zones  or  minor  faultings.  In  the  various  mountain- 
making disturbances  these  masses  acted  as  units  somewhat  as 
would  the  blocks  of  a pavement  if  it  were  thrown  into  undula- 
tions. As  a result  of  these  movements  of  adjustment  along  the 
zones  of  weakness,  the  rocks  on  both  sides  of  the  zone,  on  the 
outer  borders  of  the  masses,  have  been  rendered  gneissoid,  or, 
in  places,  almost  schistose.  In  other  places  the  rock  has  been 
sheeted  and  sheared.  The  degree  of  change  and  the  distance 
from  the  zone  of  movement  to  which  the  rock  is  affected  would 
be  roughly  proportional  to  the  magnitude  of  the  force. 

The  mineral  composition:  The  rock  is  an  ordinary  biotite 
granite,  with  occasional  hornblende  crystals.  The  feldspar  is 
mainly  orthoclase,  and  in  the  distinctly  granitic  part  of  the 
rock  is  the  most  important  constituent.  As  the  gneissoid  char- 
acter becomes  prominent,  the  relative  importance  of  the  min- 
erals changes,  and  quartz  becomes  increasingly  important.  A 
few  granite  masses,  probably  intrusions,  show  a porphyritic  tex- 
ture in  which  the  feldspars  reach  from  one-half  inch  to  an  inch 
in  length.  The  quartz  is  in  irregular  grains  and  varies  in 
amount,  but  in  the  massive  granite  makes  up  probably  about 
twenty  per  cent,  of  the  rock.  The  biotite  of  the  fresh  rock  is 
in  tabular  crystals  twice  or  three  times  as  broad  as  thick,  and 
forms  perhaps  eight  per  cent,  of  the  rock. 


18 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Weathering : The  rate  of  weathering  depends  quite  largely 
upon  the  structure  and  texture  of  the  rock.  The  more  dis- 
tinctly gneissoid  forms  weather  most  rapidly,  and  the  massive 
granite  least  rapidly.  This  fact  expresses  itself  in  the  topo- 
graphy. In  many  places  the  more  massive  granite  forms  rather 
prominent  knobs  and  bosses,  and  a large  percentage  of  the 
boulders  of  decay  are  granite.  Occasionally,  where  the  meta- 
morphism has  rendered  the  rock  unusually  rich  in  quartz,  the 
gneiss  is  quite  as  resistant  as  the  granite.  In  the  weathering 
of  the  gneissoid  forms,  the  mica  segregated  in  bunches  and  min- 
ute lenses  and  irregular,  discontinuous  planes  is  the  first  min- 
eral to  yield.  It  forms  a rusty  green  chloritic  mineral  which 
is  very  soft,  inelastic  and  brittle.  The  weakening  along  these 
planes  causes  very  rapid  granular  disintegration  of  the  rock. 
This  is  still  more  marked  in  the  sheeted  and  closely  jointed 
rocks.  The  massive  form  shows  a tendency  to  weather  into 
rounded  boulders,  knobs  and  prominences  by  the  slow  and  uni- 
form penetration  of  the  agencies  of  weathering.  The  coarse 
grained  rock  weathers  more  rapidly  than  the  fine  grained. 

Origin:  The  intrusive  character  of  a large  part,  possibly  all 
of  the  granite  and  gneissoid  granite,  is  evident  from  the  field 
relations.  Small  bodies  of  hornblende-mica-schist  and  horn- 
blende-schist of  a dark-gray  to  almost  black  color,  and  rather  low 
quartz  content  are  quite  numerous,  and  were  evidently  torn 
from  an  older  formation  through  which  the  granite  found  its 
way  to  the  surface.  The  contact  with  the  gneiss  is,  in  places 
characteristically  an  eruptive  contact.  Blocks  of  gneiss  were 
caught  up  and  surrounded  by  the  granite,  and  arms  and  dike- 
like bodies  of  granite  penetrate  the  gneiss,  following  and  filling 
fissures  formed  at  the  time  of  the  intrusion.  In  a few  places 
traces  of  contact  metamorphism  are  noticeable  in  the  develop- 
ment  of  garnets  and  other  minerals.  In  other  places  there  are 
veinlets  and  stringers  of  very  fine  grained  rock  resulting  from 
the  rapid  cooling  of  the  molten  granite  in  contact  with  the  cold 
rock  into  which  it  was  intruded. 

GNEISS. 

This  rock  is  older  than  the  granite,  and,  judging  by  the  great 
degree  of  metamorphism  it  has  undergone  as  compared  with  the 
granite,  it  is  very  much  older.  It  lies  mainly  in  the  western  and 
northwestern  parts  of  the  tungsten  field.  Within  the  gneiss  area, 
rocks  of  all  structures  may  be  found,  from  massive  granite  to  a 
perfectly  laminated  schist,  but  the  prevailing  type  is  the  gneiss. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


19 


The  typical  rock  has  the  general  composition  of  a biotite  granite, 
but  the  proportion  of  the  different  minerals  varies  widely,  par- 
ticularly across  the  strike  of  the  structure.  In  places  the  rock 
can  scarcely  be  distinguished  from  the  granite,  either  in  compo- 
sition or  structure,  while  in  others  the  proportion  of  feldspar 
has  greatly  decreased,  and  that  of  the  quartz  has  correspondingly 
increased.  Other  areas  will  show  quartz  and  biotite,  almost  to 
the  exclusion  of  feldspar.  This  rock  frequently  shows  an  ad- 
vanced gneissoid,  or  even  a schistose  structure.  While  such  tran- 
sitions to  the  schist  are  by  no  means  rare,  the  schist  is  usually 
in  narrow  bands  which  soon  give  way  to  the  gneiss.  Small  areas 
of  hornblende-gneiss-schist  also  occur.  Attempts  were  made  to 
map  the  schists,  but  it  was  found  impossible  to  represent  them 
satisfactorily  on  a map  of  the  scale  here  used. 

Structural  features:  In  many  places,  as,  for  example,  on  the 
south  side  of  Boulder  Creek  at  Nederland,  and  on  the  north  side 
of  Beaver  Creek,  the  dip  and  strike  <5f  the  gneissoid  structure  are 
regular  and  well  defined  over  considerable  areas.  But  there  is 
no  general  uniformity  or  agreement  of  dip  and  strike  for  the 
region  as  a whole.  Areas  which  are  apparently  continuous  show 
wide  diversity  of  dip  and  strike.  This  discordance  may  be  due 
to  movements  of  rotation  and  tilting  during  mountain-making 
disturbances  or  at  the  time  of  the  great  granite  intrusions  of 
the  eastern  side  of  the  field.  West  of  the  tungsten  area  toward 
the  range  there  seems  to  be  a greater  regularity  of  dip  and  strike. 

Origin : No  absolute  proof  of  the  origin  of  the  gneiss  can  be 
offered,  but  the  following  facts  are  in  keeping  with  the  view  that 
it  is  derived  from  sediments.  The  broader  bands  of  the  gneiss 
differ  widely  in  composition.  One  may  be  almost  entirely  mica 
and  quartz  while  its  contact  neighbor  may  be  a granite  except 
for  structure.  Again,  a granitic  band  may  lie  against  one  in 
which  quartz  may  equal  all  other  minerals  together.  Another 
band  may  show  a considerable  development  of.  fibrolite  while  its 
contact  neighbor  may  show  none.  These  differences  of  mineral 
composition  suggest  such  differences  of  original  composition  as 
may  be  found  in  successive  strata  of  a sedimentary  series.  The 
regularity  of  the  dip  and  strike  of  the  gneissoid  lamination  sug- 
gests stratification.  The  fact  that  a few  miles  west  on  the  slopes 
of  Arapahoe  Peaks  there  is  a strong  band  of  fine  quartzite  con- 
forming in  dip  and  strike  to  the  structure  of  the  gneiss  in  which 
it  occurs,  suggests  a sedimentary  origin  for  the  containing  rock 
which  is  lithologically  and  structurally  similar  to  the  gneiss  of 


20 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


the  tungsten  field.  Again,  about  two  miles  to  the  east  of  the 
field  on  South  Boulder  and  Coal  Creeks,  there  is  a great  quartzite 
and  schist  series  below  the  Paleozoic  sediments,  and  in  contact 
with  the  granite-gneiss  series.  The  schists  associated  with  the 
quartzite  are  so  related  to  it  that  it  is  hardly  possible  to  doubt 
their  sedimentary  origin.  On  both  sides  of  the  area  we  have 
metamorphic  rocks  derived  from  sediments.  Between  these  lies 
the  great  granite  and  gneissoid-granite  series  which  is  in  eruptive 
contact  with  the  quartzite  on  the  east  and  the  gneiss  containing 
the  quartzite  to  the  west.  The  general  relations  are  consistent 
with  the  thought  of  a great  metamorphic-sedimentary  group  in- 
truded by  a vast  wedge  of  granite  which  has  widely  separated 
the  two  parts  of  the  series.  A great  series  of  quartzites,  quartz- 
mica  schists  and  mica  schists  similar  to  that  of  Coal  Creek  is 
cut  by  the  canyon  of  the  Big  Thompson  River  in  Larimer  County. 

FINE-GRAINED  GRANITE. 

Within  the  granite  area,  a fine-grained  biotite  granite  occurs 
in  numerous  masses,  of  which  the  largest  exposure  is  shown  on 
the  map,  about  a mile  northeast  of  Nederland.  The  same  rock 
occurs  near  by  in  masses  often  but  a few  feet  across,  and  in  con- 
siderable amount  between  Magnolia  and  South  Boulder  Creek. 

The  rock  is  distinctly  gneissoid,  and  where  it  occurs  on  the 
border  of  the  ancient  gneiss  there  is  generally  no  well-defined 
contact  between  the  two,  owing  to  the  fact  that  they  have  under- 
gone a high  degree  of  metamorphism  which  has  developed  pro- 
nounced directional  structure  in  both.  Specimens  taken  from 
mines  usually  show  the  mica  to  be  leached  out  and  the  feldspar 
more  or  less  kaolinized.  In  this  state  the  rock  might  at  first 
glance  be  taken  for  aplite.  The  fine-grained  variety  is  cut  by 
pegmatite  dikes  usually  narrower  than  those  cutting  the  coarser 
granite.  This  rock  will  be  further  described  in  connection  with 
the  ore  bodies. 

PEGMATITE. 

Pegmatite,  both  coarse  and  fine,  is  very  abundant  throughout 
the  tungsten  field.  The  relations  of  the  dikes  (and  veins)  to  the 
country  rock  indicate  two  modes  of  origin.  There  are  some 
dikes  which  have  been  formed  in  much  the  same  manner  as  dikes 
are  generally  formed — by  the  filling  of  fissures  with  molten  or, 
at  least,  highly  plastic  rock.  Whether  the  mass  was  in  a state 
of  aqueo-igneous  fusion  (or  in  mineral  solution),  water  playing 
an  important  role,  is  not  easily  determined.  Certain  it  is  that 
in  places  the  mass  had  sufficient  density  to  pluck  off  and  hold 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


21 


suspended  large  blocks  of  the  country  rock,  and  that  the  country 
rock  itself  was  solid  enough  to  break  with  sharp  angular  outlines 
and  retain  its  form  even  when  surrounded  by  the  pegmatite  mass. 
That  some  of  these  dikes  are  contemporaneous  with  the  solidifica- 
tion of  the  containing  rocks  seems  very  improbable.  Erosion  has 
removed  a very  considerable  thickness  from  the  surface  of  the 
country,  and  the  parts  of  the  dikes  now  exposed  must  have  been 
formed  at  no  small  depth.  But  these  plucked-off  masses  of  coun- 
try rock  are  found  in  the  deeper  workings  of  the  mines.  At  the 
same  time  there  is  rarely  any  evidence  of  contact  metamorphism 
between  the  blocks  and  the  containing  pegmatite  or  the  country 
rock  and  the  pegmatite.  Occasionally  the  pegmatite  dikes  are 
bordered  by  a few  inches  of  country  rock  containing  little  or  no 
dark  mineral,  and  consequently  of  lighter  color  than  that  a 
little  further  from  the  contact.  This  difference  in  composition 
is  probably  due  to  subsequent  solution  and  replacement  rather 
than  to  contact  metamorphism.  Textural  variation  from  the 
wall  toward  the  center  of  the  dikes  is  noticeable.  The  dikes  have 
well-defined  walls  and  generally  regular  courses. 

There  are  other  veins,  or  irregular  bodies,  of  pegmatite, 
mostly  of  finer  texture,  but  still  noticeably  coarser  than  the 
containing  rock,  which  have  had  an  entirely  different  origin. 
They  are  the  result  of  a process  of  solution  and  recrys- 
tallization of  the  country  rock  along  seams  and  fracture  lines. 
These  bodies  never  have  well-defined  boundaries,  but  show  a grad- 
ual transition  to  the  texture  and  mineral  composition  of  the  coun- 
try rock.  The  pegmatization  frequently  follows  branching  and 
rebranching  fractures  and  penetrates  the  country  rock  irregularly 
on  the  two  sides  of  the  fractures,  not  infrequently  resulting  in  the 
alteration  of  two-thirds  of  the  rock  volume.  This  type  of  pegma- 
tite is  particularly  common  in  association  with  the  ore  bodies, 
and  does  not  appear  to  be  abundant  elsewhere,  although  it  may 
be  found  in  parts  of  the  field  away  from  known  ore  bodies. 

The  coarse  and  fine  pegmatites  occurring  in  dike  form  are 
younger  than  the  containing  rocks,  and  though  they  do  not  belong 
to  the  latest  period  of  movement  and  igneous  activity,  have  suf- 
fered but  little  crushing.  Three  distinct  periods  of  faulting  have 
left  their  records  in  many  of  the  dikes  with  which  the  ores  are 
associated.  The  movements  do  not  appear  to  have  been  great.  In 
some  instances  the  faulting  and  its  accompanying  phenomena  fol- 
low one  wall  of  the  dike,  while  in  others  movement  has  occurred 


22 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


on  both  sides,  and  in  a few  the  crushing  and  movement  have  in- 
volved the  whole  dike.  Rarely  do  the  crushing  and  brecciation 
extend  far  into  the  country  rock.  Occasionally,  however,  the 
fault  breccia  contains  much  country  rock.  Both  tension  and 
compression  movements  have  occurred,  and  the  brecciation  is 
probably  more  largely  due  to  the  latter  than  to  the  former. 

The  topographic  effect  of  the  pegmatite  bodies  is  readily  ob- 
servable in  both  gneiss  and  granite,  where  it  frequently  forms 
ridges  or  knobs  on  account  of  its  greater  resistance  to  weathering. 
Occasionally,  however,  the  course  of  a pegmatite  body  may  be 
known  only  by  the  debris  on  the  surface.  While  the  greater 
part  of  this  type  of  pegmatite  occurs  in  dikes,  irregular,  lenticu- 
lar, and  plug-like  bodies  are  quite  common.  These  forms  do  not 
show  such  definite  boundaries  as  do  the  dikes. 

Mineral  composition : In  the  order  of  their  importance,  the 
minerals  of  the  regular  pegmatite  bodies  are : Microcline,  ortho- 
clase,  (possibly  albite),  quartz,  biotite  and  muscovite.  In  some 
dikes  and  parts  of  dikes  the  feldspar  may  form  almost  the  entire 
mass,  while  in  other  places  quartz  is  the  dominant  mineral.  Black 
mica  is  rarely  important — seldom  reaching  one  per  cent,  of  the 
volume  of  the  rock.  Muscovite  is  remarkably  irregular  in  its  gen- 
eral distribution.  In  certain  small  sections  of  a few  dikes  it  may 
form  from  five  to  ten  per  cent,  of  the  rock  and  be  uniformly  dis- 
tributed. In  other  cases  it  is  more  or  less  segregated  near  the 
walls  of  the  dikes.  In  two  pegmatite  dikes  to  the  north  of  the 
tungsten  area  muscovite  is  locally  developed  and  segregated  to 
such  an  extent  that  two  or  more  mica  prospects  have  been  located 
on  them.  In  many  dikes  quartz  is  much  more  abundant  in  the 
middle  one-third  than  in  the  outer  parts.  A few  show  distinct 
banding,  though  it  is  rarely  so  well  defined  as  that  often  found 
in  vein  structure. 

The  central  band  is  generally  quartz,  and  masses  ranging 
from  two  or  three  to  twenty-five  feet  in  diameter  are  found.  In 
these  cases  the  dike  locally  resembles  a strong  quartz  vein. 
Graphic  granite  occurs  sparingly. 

Small  acid  granite  veins,  ranging  in  width  from  a fraction 
of  an  inch  to  a few  inches,  are  common  in  both  the  gneissoid 
granite  and  the  gneiss.  They  are  composed  of  feldspar  and  quartz 
with  occasionally  a meager  sprinkling  of  biotite,  and  less  com- 
monly muscovite.  Their  composition  and  their  relation  to  the 
containing  rocks  indicate  an  origin  similar  to  that  of  the  pegma- 
tites. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


23 


Rare  minerals  and  minerals  in  whose  formation  heated 
vapors  and  gases  play  an  important  part  are  characteristic  of 
many  pegmatite  occurrences.  But  they  are  notably  absent  from 
the  Boulder  pegmatites.  Ores  of  tin,  antimony,  molybdenum  and 
tungsten  are  also  looked  for  in  pegmatites.  But  in  this  region, 
with  the  possible  exception  of  a very  occasional  tourmaline  crys- 
tal, and  the  doubtful  occurrence  of  fluorite,  the  tungsten  ores 
occur  alone. 

t INTRUSIVE  ROCKS. 

By  R.  D.  Crawford. 

The  intrusive  rocks  are  almost  entirely  confined  to  interme- 
diate and  basic  types.  Excepting  the  pegmatite  and  aplite,  rock 
of  high  acidity  is  found  in  only  one  dike,  probably  in  small  quan- 
tity, and  as  a differentiation  product.  Andesites  predominate, 
but  their  near  relatives,  the  latites  and  dacites,  on  the  one  hand, 
and  basic  rocks  on  the  other,  are  well  represented.  The  dikes 
are  generally  narrow;  perhaps  the  majority  are  less  than  20 
feet  wide,  and  a few  less  than  3 feet.  They  can  usually  be  fol- 
lowed by  their  outcrops  without  difficulty,  but  are  often  greatly 
weathered. 

The  general  trend  of  the  dikes  in  the  productive  tungsten 
area  is  east  and  west.  In  the  vicinity  of  the  old  Boulder  County 
Mine  and  southward  they  are  most  numerous,  but  many  of  these 
are  narrow  and  pinch  out  a short  distance  west  of  the  boundary 
'vf  the  map.  From  Bald  Mountain  northward  the  dikes  widen 
greatly,  and  trend  nearly  north  and  south. 

Field  relations  furnish  but  little  evidence  of  the  relative  age 
of  the  different  dikes.  Since  the  diabase  is  cut  by  a latite  dike, 
perhaps  an  offset  of  the  Sugarloaf  dike,  it  is  older  than  the  lat- 
ter rock.  The  limburgite  appears  to  cut  the  diabase,  but  the  ex- 
posure at  the  intersection  of  the  two  dikes  is  not  very  distinct. 
All  the  intrusive  dikes  are  younger  than  the  pegmatite.  No 
other  field  observations  made  help  to  determine  the  succession. 
A light  gray  kaolinized  dike  rock,  probably  the  felsite  described 
below,  occurs  in  the  Beddick  Mine,  but  does  not  reach  the  sur- 
face. The  dike  cuts  the  granite,  but  was  intruded  prior  to  the 
deposition  of  the  ore. 

In  addition  to  the  dike  rocks  described  below,  boulders  of 
monzonite  occur  on  the  steep  slopes  of  Eldora  Mountain  near  the 
west  border  of  the  area.  These  blocks  may  not  be  far  from 
their  original  position,  but  it  is  possible  that  they  have  fallen 
from  the  moraines  above. 


24 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Andesites. 

Hornblende  andesite : In  the  dikes  with  a general  east-west 
trend  in  the  vicinity  of  Nederland,  and  as  far  east  as  Bald  Moun- 
tain, the  andesite  is  fairly  uniform  in  texture  and  mineral  com- 
position. It  is  commonly  medium  to  light  gray,  usually  with  a 
greenish  tinge.  It  is  seldom  found  quite  fresh  or  dark  in  color. 
Although  the  phenocrysts  are  generally  small,  the  rock  is  in- 
variably porphyritic,  with  the  larger  crystals  not  infrequently 
about  equal  in  amount  to  the  ground-mass.  Feldspar  pheno- 
crysts are  greatly  in  excess  of  hornblende  phenocrysts,  and  are 
commonly  1 to  3 mm.  in  diameter,  though  an  occasional  crystal 
may  reach  5 or  6 mm.  Ordinarily  the  hornblendes  are  less  than 
1 mm.  in  thickness,  with  a length  of  2 to  4 mm. 

Thin  sections  show  that  the  phenocrystic  feldspars  are 
mainly  andesine,  but  labradorite  may  sometimes  be  present.  The 
hornblende  is  the  common  green  variety  with  strong  pleochroism. 
The  felty  groundmass  is  composed  largely  of  poorly  individual- 
ized feldspar  laths,  with  interstitial  feldspar  and  grains  of  mag- 
netite. A few  flakes  of  biotite  are  present  in  occasional  speci- 
mens. These  minerals,  together  with  minute  crystals  of  apatite 
enclosed  in  the  phenocrysts  and  groundmass,  are  the  only  pri- 
mary constituents  now  determinable.  Kaolin,  calcite,  chlorite, 
epidote,  quartz  and  iron  oxides  are  present  in  variable  amounts 
as  alteration  products. 

The  hornblende  andesite  dikes  with  a northward  trend,  in 
the  vicinity  of  Bald  and  Sugarloaf  mountains,  differ  from  those 
described  chiefly  in  color  and  in  the  quantity  of  biotite.  These 
andesites  range  from  very  dark  to  very  light  grey,  but  the  green- 
ish cast  so  common  in  the  dikes  described  above  is  usually  lack- 
ing. Hornblende  is  here,  also,  the  principal  ferromagnesian  con- 
stituent, but  biotite  very  frequently  is  present  in  crystals  often 
rounded  by  re-solution.  Phenocrystic  orthoclase  appears  in 
small  amount. 

Glassy  hornblende  andesite:  This  is  a dense  black  rock, 
basaltic  in  appearance,  with  numerous  hornblende  phenocrysts 
and  less  numerous  feldspars.  Weathering  makes  the  phenocrysts 
conspicuous,  and  brings  out  the  fluxional  arrangement  of  the 
hornblendes,  which  are  commonly  under  6 or  7 mm.  in  length. 

Under  the  microscope  the  feldspar  phenocrysts  prove  to  be 
largely  labradorite.  The  hornblende  is  brownish-green,  and  re- 
sembles the  basaltic  type.  It  occurs  also  in  microscopic  crystals 
in  the  ground  mass  with  a few  minute  octahedrons  of  magnetite. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


25 


The  ground  mass  varies  in  different  specimens  from  glassy  to 
microcrystalline.  In  the  latter  there  are  multitudes  of  lath- 
shaped feldspar  microlites  and  grains  of  magnetite  in  a glassy 
base.  Minute  apatite  crystals  are  present  in  both  the  glassy  and 
microcrystalline  varieties. 

Mica  andesite : This  variety  is  dark  brownish-gray,  with 
texture  very  similar  to  the  holocrystalline  hornblende  andesites, 
but  biotite,  instead  of  an  accessory,  is  the  most  abundant  ferro- 
magnesian  constituent.  It  occurs  in  shiny  flakes,  commonly  un- 
der 1 mm.  in  diamenter.  Prismatic  crystals  of  what  appears  to 
have  been  hornblende  are  now  completely  replaced  by  secondary 
minerals — calcite,  kaolin  and  iron  ores.  Under  the  microscope 
the  felty  groundmass  does  not  differ  materially  from  the  others 
described.  The  feldspar  phenocrysts  are  nearly  all  plagioclase, 
but  the  rock  is  a close  relative  of  the  latite  of  Sugarloaf  Moun- 
tain. In  the  short  dike  west  of  Farewell  Gulch  augite  occurs  in 
considerable  amount. 

Pyroxene  andesite : There  are  two  distinct  varieties  of  rock 
designated  on  the  map  as  pyroxene  andesite:  (1)  That  of  the 
dike  crossing  the  railroad  on  the  south  slope  of  Bald  Mountain; 
(2)  that  of  the  dikes  in  the  vicinity  of  Beaver  Creek. 

The  Bald  Mountain  type  is  rather  dark  grey,  and  carries  a 
few  small  pyroxenes  and  fewer  feldspar  phenocrysts  in  a felsitic 
groundmass.  But  few  phenocrysts  of  either  mineral  have  a 
length  of  2 mm.  Under  the  microscope  multitudes  of  lath-shaped 
feldspar  with  fluxional  arrangement  are  seen.  Though  not  many 
are  5 mm.  long,  they  are  almost  all  twinned  after  the  albite  or 
the  Carlsbad  law,  or  both.  Extinction  angles  (with  a maximum 
of  30°)  indicate  andesine-labradorite.  The  few  phenocrysts  may 
be  somewhat  more  acid,  but  all  are  plagioclase.  The  pyroxene 
phenocrysts,  and  many  smaller  crystals  and  formless  grains,  are 
colorless  augite,  but  the  large  proportion  of  small  idiomorphic 
crystals  of  pyroxene  with  parallel  extinction  suggests  the  pres- 
ence of  an  orthorhombic  variety.  Many  small  magnetite  crystals 
and  a few  apatites  are  present.  Nearly  or  quite  all  the  interesti- 
tial  base  is  anisotropic  and  apparently  largely  feldspar. 

In  the  freshest  exposures  of  the  dikes  in  the  vicinity  of 
Beaver  Creek,  provisionally  called  pyroxene  andesite,  the  sur- 
faces of  joint  blocks  are  generally  reddish,  but  the  interior  is 
greenish-gray.  The  most  striking  feature  is  the  great  abundance 
of  feldspar  phenocrysts  with  about  one-twentieth  as  many  pheno- 
crysts of  augite.  Phenocrysts  ( of  these  two  minerals  compose 


26 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


approximately  half  the  rock.  The  feldspars  are  commonly  2 to  4 
mm.  in  diameter,  bluish-gray  in  color,  and  usually  without  meg- 
ascopic striae.  The  augite  crystals  are  1 to  4 mm.  in  thickness. 

In  thin  section  the  feldspar  phenocrysts  are  seen  to  be  plagio- 
clase,  in  large  part  labradorite,  but  apparently  ranging  from 
andesine  to  bytownite.  The  augite  is  pale  green  to  coloress,  and 
is  frequently  chloritized.  Olivine  occurs  as  an  accessory  in  small 
but  well-formed  crystals,  usually  serpentinized.  Serpentine  is 
also  scattered  throughout  the  groundmass  in  considerable 
amount.  Stout  apatite  crystals  are  not  rare.  Magnetite  crystals 
are  fairly  common.  The  microcrystalline  groundmass  is  com- 
posed almost  entirely  of  feldspar  in  lath  forms  and  irregular 
grains.  The  microlites  are  often  once  twinned,  and  many  are 
doubtless  plagioclase.  In  some  specimens  they  appear  to  have 
undergone  recrystallization. 

Feldspar  probably  composes  80  per  cent,  to  90  per  cent,  of 
the  rock  which  is  apparently  the  aphanitic  equivalent  of  anortho- 
site. It  may  be  considered  a transition  form  closely  related  to 
Ihe  basalts.  When  material  is  found  sufficiently  fresh  to  war- 
rant minute  study,  a more  detailed  description  will  be  given. 

Felsite. 

The  felsite  is  bluish-gray  in  the  least  weathered  exposures, 
but  ordinarily  it  is  almost  white  through  kaolinization.  Black 
or  greenish  prismatic  phenocrysts  of  hornlende  or  its  altera- 
tion products  can  be  seen  in  the  less  weathered  varieties, 
becoming  very  noticeable  when  the  surface  of  the  rock  is 
wet.  A few  phenocrysts  of  feldspar  1 or  2 mm.  in  diameter  can 
be  seen  in  the  fresher  specimens,  but  are  completely  replaced  by 
kaolin  in  the  more  altered  rock. 

In  thin  section  some  of  the  feldspars  retain  traces  of  poly- 
synthetic twinning,  but  more  frequently  a trace  of  Carlsbad 
twinning.  Whether  or  not  all  were  plagioclase  it  is  impossible 
to  say.  The  hornblende  has  lost  almost  completely  its  primary 
character.  The  groundmass  is  composed  largely  of  irregular 
grains  and  lath-shaped  feldspar  microlites,  with  considerable 
hornblende  and  secondary  material.  The  microlites  of  feldspar 
are  often  once  twinned.  The  rock  is  probably  andesite,  but  since 
it  is  distinctly  different  in  textural  character  from  the  other 
andesites  in  the  district,  and  since  there  is  much  uncertainty 
as  to  the  mineral  composition,  it  seems  best  to  retain  the  field 
term  “felsite,” 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  27 

Dacite. 

The  dacite,  or  quartz  andesite,  is  very  similar  in  color  and 
texture  to  the  hornblende  andesites  in  the  vicinity  of  Neder- 
land. Phenocrysts  of  feldspar  and  biotite  make  up  about 
half  the  rock.  The  biotite  is  abundant  in  shiny  flakes 
usually  about  1 mm.  in  diameter,  or  less.  The  unaided  eye  can 
detect  an  occasional  hornblende  crystal.  A few  quartz  pheno- 
crysts 1 to  2 mm.  in  diameter  can  be  seen.  They  are  more  evident 
in  the  weathered  rock,  which  is  otherwise  similar  to  the 
weathered  andesite. 

In  thin  sections  quartz  phenocrysts  are  numerous,  invariably 
in  rounded  forms  resulting  from  re-solution.  The  biotite  often 
shows  the  characteristic  hexagonal  outline.  The  feldspar  pheno- 
crysts are  plagioclase.  What  has  been  said  above  in  regard  to 
the  accessory  and  secondary  minerals  and  felty  groundmass  of 
the  holocrystalline  hornblende  andesite  applies  to  this  rock  prac- 
tically without  modification. 

The  very  short  dike  near  the  road,  about  a quarter  of  a mile 
southeast  of  the  old  Boulder  County  mine,  apparently  carries 
much  more  hornblende  than  the  other  dacite  dikes.  It  is  badly 
altered  and  no  microscopic  determinations  were  made. 

Latite. 

Latite  occurs  in  far  greater  amount  not  far  north  of  this 
region.  The  strongest  dike  in  the  area  mapped  passes  through 
Sugarloaf  Mountain,  where  it  reaches  a width  of  perhaps  60 
feet  or  more,  and  has  been  in  large  measure  responsible  for 
the  development  of  the  peak.  The  rock  from  this  dike  was  once 
described  as  andesite,1  but  inasmuch  as  it  contains  a large 
amount  of  orthoclase  and  passes  into  a trachyte  toward  the 
northeast,  it  seems  best  to  consider  it  latite  throughout  the  en- 
tire length  of  the  dike.  The  chemical  analysis2  indicates  its 
trachytic  character,  or  position  intermediate  between  andesite 
and  trachyte. 

The  rock  contains  numerous  phenocrysts  of  feldspar  and 
biotite,  less  abundant  pyroxene  and  hornblende,  and  a few  crys- 
tals of  titanite.  Feldspar,  in  white,  sometimes  glassy  crystals 
usually  less  than  2 mm.  in  diameter,  is  by  far  the  most  impor- 
tant phenocrystic  mineral.  Biotite  flakes  are  commonly  less 

lHogarty,  Barry,  Proceedings  of  the  Colorado  Scientific  Society,  Vol.  VI., 
pp.  173-185. 

2lbld.,  p.  181. 


28  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

than  1 mm.  in  diameter.  The  hornblende  and  pyroxene  prisms 
are  usually  not  more  than  3 mm.  long. 

The  microscope  shows  the  ratio  of  plagioclase  to  orthoclase 
to  be  about  2 to  1,  and  the  plagioclase  to  be  largely  andesine. 
The  biotite  is  often  in  perfect  crystals,  generally  with  a border 
suggesting  re-solution. 

Pyroxene  ranks  next  to  biotite  in  amount.  It  is  pale  green, 
weakly  pleochroic,  and  has  the  extinction  angle  of  augite.  The 
hornblende  is  the  common  green  variety  with  strong  pleochro- 
ism.  Almost  invariably  the  crystals  show  a re-solution  border. 
Titanite  appears  as  a constant  accessory  in  idiomorphic  crystals. 
The  felty  groundmass  is  composed  of  poorly  individualized  feld- 
spar microlites  with  interstitial  quartz  and  possibly  feldspar, 
besides  numerous  grains  of  magnetite  and  much  secondary  cal- 
cite.  The  quartz  is  probably  chiefly  secondary.  The  feldspar 
microlites  are  often  once  twinned,  and  have  parallel  extinction. 
Practically  all  of  the  original  constituents  show  much  altera- 
tion. 

The  dike,  about  a mile  east  of  Rollinsville,  is  provisionally 
mapped  as  latite  until  fresher  material  than  that  at  present 
available  for  examination  may  be  found.  In  the  freshest  ex- 
posures observed  the  rock  is  greenish  or  reddish,  with  feldspar 
phenocrysts  in  only  moderate  numbers,  and  fewer  augite  crys- 
tals. Under  the  microscope  magnetite,  chlorite  and  calcite  ap- 
pear in  the  groundmass,  which  seems  to  be  composed  largely 
of  recrystallized  or  secondary  feldspar.  The  phenocrysts  are 
badly  altered,  but  a few  appear  to  be  orthoclase. 

Latite  Porphyry. 

The  long  east-west  dike  passing  through  the  high  points 
north  of  Beaver  and  South  Boulder  creeks  and  Winiger 
Gulch  is  of  interest  chiefly  because  of  the  variety  that  it 
presents.  It  can  usually  be  traced  only  by  means  of  surface 
boulders.  Not  one  good  exposure  occurs,  and  the  few  shallow 
prospect  holes  do  not  uncover  the  full  width  of  the  dike.  Al- 
though distinct  gradations  probably  exist,  there  is  no  oppor- 
tunity to  observe  them  in  the  field,  and  hence  for  purposes  of 
description  it  seems  best  to  consider  the  characteristic  varieties 
separately.  Along  the  line  of  the  dike,  boulders  of  two  or 
three  varieties  are  usually  found,  and  their  disposition  gives 
no  clue  to  the  arrangement  of  the  different  kinds  of  rock  in 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  29 

place,  but  it  is  possible  that  several  instrusions  have  followed  the 
same  line  of  weakness. 

The  variety  which  perhaps  occurs  in  greatest  abundance, 
ranges  from  a rock  composed  almost  entirely  of  feldspar  pheno- 
crysts  1 to  2 mm.  in  diameter,  with  practically  no  groundmass,  to 
a phase  in  which  part  of  the  phenocrysts  reach  8 or  10  mm. 
in  diameter,  while  the  groundmass  makes  up  about  two-thirds 
of  the  rock.  The  freshest  specimens  are  bluish-gray  in  color, 
and,  in  addition  to  the  lustrous  feldspars,  contain  many  small 
patches  of  kaolin  and  iron  oxides  replacing  hornblende.  More 
weathered  specimens  are  pinkish  white  and  white,  containing 
numerous  fresh  feldspars,  and  show  many  small  cavities  from 
which  some  mineral  has  been  dissolved. 

Under  the  microscope  the  feldspars  are  seen  to  be  both 
orthoclase  and  acid  plagioclase,  with  the  latter  in  excess  in  part 
of  the  rock,  and  again  almost  disappearing  from  some  specimens 
with  much  groundmass,  when  the  rock  becomes  a typical 
trachyte.  In  the  phase  which  is  nearly  devoid  of  groundmass, 
the  two  kinds  of  feldspar  show  examples  of  perthitic  inter- 
growth, and  a number  of  the  orthoclases  enclose  plagioclase  in 
poikilitic  manner.  In  some  sections  small  crystals  of  biotite  are 
present  and  the  same  mineral,  in  aggregates  of  minute  flakes, 
occasionally  replaces  some  primary  constituent.  The  ground- 
mass  is  composed  largely  of  small  grains  of  unstriated  feldspar 
and  a little  quartz,  the  latter  in  large  part  secondary. 

Another  phase  contains  phenocrysts  of  sanidine  up  to  15 
mm.  in  diameter,  with  a multitude  of  smaller  feldspar  crystals, 
the  majority  of  which  are  plagioclase.  Zircon  and  apatite  are 
present  as  inclusions.  Hornblende  and  its  alteration  products 
occur  as  in  the  variety  described  above. 

A quartz-bearing  latite  porphyry  may  be  considered  to  rep- 
resent a transition  toward  the  rhyolite  porphyry  described  be- 
low. It  contains  feldspars  of  three  periods  of  crystallization. 
Of  the  first  period  there  are  comparatively  few  orthoclase 
phenocrysts  with  a maximum  length  of  2 cm.  In  the  second 
generation  both  orthoclase  and  plagioclase  occur  in  rectangular 
forms  1 or  2 mm.  across,  with  plagioclase  in  excess.  The 
groundmass  contains  the  feldspars  of  the  third  period,  which 
in  thin  section  are  seen  to  be  formless  grains  of  orthoclase.  The 
naked  eye  can  also  detect  many  small  flakes  of  biotite  which 


30  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

are  microscopically  seen  to  be  both  primary  and  secondary. 
Quartz  occurs  in  small  phenocrysts  corroded  by  the  groundmass, 
of  which  it  contains  numerous  inclusions. 

Boulders  of  soda-rhyolite-porphyry  can  be  found  almost  the 
entire  length  of  the  dike,  often  in  great  abundance.  Numer- 
ous phenocrysts  of  quartz,  feldspar  and  biotite  occur  in 
a granular  groundmass.  The  largest  feldspar  phenocrysts, 
which  are  practically  all  orthoclase,  stand  out  conspicuously 
on  weathered  surfaces.  They  are  from  1 to  2.5  cm.  long,  and 
make  up  one-fourth  to  one-half  the  rock.  Quartz  phenocrysts 
leach  a diameter  of  7 or  8 mm.,  but  are  usually  smaller.  They 
are  commonly  rounded  and  very  irregularly  distributed,  varying 
from  almost  none  to  15  per  square  inch  of  surface.  This  in- 
constancy in  distribution  in  a rock  with  both  orthoclase  and 
plagioclase  is  the  best  evidence  we  have  that  the  rhyolite  and 
quartz  free  latite  are  phases  of  a single  intrusion.  Biotite  is 
not  seen  in  all  specimens,  but  may  be  quite  abundant  locally  in 
flakes  2 mm.  or  less  in  diameter. 

The  microscope  shows  orthoclase  and  plagioclase  pheno- 
crysts of  medium  size.  Crystal  outlines  are  generally  distinct, 
but  the  crystals  have  suffered  grinding  anc(  crushing  at  the 
margin  and  are  sometimes  broken  in  two.  The  quartz  pheno- 
crysts show  no  crystal  outline,  and  have  been  subjected  to  simi- 
lar grinding.  Zircon  and  apatite  are  enclosed  by  the  quartz 
and  feldspars.  The  groundmass  is  a holocrystalline  aggregate 
of  quartz,  orthoclase  and  plagioclase. 

The  short  dike  of  latite  porphyry  in  Farewell  Gulch  contains 
sanidine  phenocrysts  up  to  2 cm.  across,  together  with  many 
smaller  crystals  of  both  orthoclase  and  plagioclase  in  a much 
filtered  groundmass. 


Diabase. 

This  rock  occurs  in  only  two  dikes  within  the  area  mapped, 
the  longer  one  of  which  has  been  traced  approximately  ten 
miles  and  has  a maximum  width  of  about  70  feet.  The  dia- 
base is  dark  greenish-grey,  very  heavy  and  extremely  tough. 
Greenish-gray  lath-shaped  feldspars,  black  pyroxene  and  magne- 
tite or  ilmenite  are  the  essential  constituents,  with  pyrite  as  an 
occasional  accessory.  The  feldspar  laths  are  rarely  over  3 or 
4 mm.  long.  Pyroxene  and  the  iron  ores  are  almost  entirely  with- 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


81 


out  crystal  boundaries,  but  are  packed  in  the  interstices  among 
the  feldspars,  producing  true  diabasic  texture.  This  is  best  shown 
on  weathered  surfaces. 

In  thin  section  the  feldspar  is  seen  to  be  almost  entirely 
andesine-labradorite  with  the  usual  albite  twinning  sometimes 
combined  with  Carlsbad  twinning.  The  pyroxene  is  in  part 
augite  with  a somewhat  less  amount  of  hypersthene.  The  augite 
is  pale  brown,  and  often  uralitized  and  chloritized.  The  hypers- 
thene is  pale  yellow,  contains  the  characteristic  inclusions,  and 
is  frequently  serpentinized.  Black  iron  ore,  highly  titaniferous,  is 
abundant.  Apatite  is  a common  accessory  enclosed  by  the  other 
minerals.  Very  rarely  the  rock  is  found  in  an  approximately 
un  weathered  state. 

Lamprophyre. 

The  few  exposures  of  lamprophyre  that  occur  might  easily 
be  passed  over  in  the  field  unobserved  because  of  their  resemblance 
in  color  to  the  weathered  gneiss.  Freshest  specimens  are  green- 
ish-gray and  show  small  grains  of  feldspar  less  than  1 mm.  in 
diameter  and  a great  amount  of  epidote. 

The  microscope  shows  the  rock  to  be  a holocrystalline  aggre- 
gate of  feldspar,  epidote,  hornblende  and  magnetite,  with  apatite 
crystals  enclosed  by  the  essential  constituents.  Feldspar  makes 
up  nearly  half  of  the  rock,  both  orthoclase  and  plagioclase  being 
present.  The  extinction  angles  of  the  plagioclase  indicate  albite. 
Some  of  the  feldspars  approach  idiomorphic  forms,  but  more  are 
entirely  without  crystal  outline.  Manj>  crystals  are  partly  re- 
placed by  epidote,  the  replacement  beginning  usually  at  the  cen- 
ter of  the  crystal.  Small  prismatic,  acicular  crystals  of  amphi- 
bole  seem  to  have  crystallized  earlier  than  the  feldspars.  A trace 
of  the  orthopinacoidal  twinning  can  still  be  seen,  though  the 
mineral  is  in  great  degree  epidotized.  Epidote  occurs  in  an 
amount  equal  to  that  of  the  feldspar,  replacing  crystals  of  am- 
phibole  and  in  irregular  masses  in  and  between  the  feldspars. 
Other  secondary  minerals  in  small  quantities  are  chlorite,  serpen- 
tine and  quartz.  The  magnetite  is  perhaps  both  primary  and 
secondary. 

Basalt  and  Basalt  Porphyries.  ^ 

Basalt:  As  a rule  the  basalts  are  decidedly  porphyritic,  but 
a few  dikes  occur  which  cannot  properly  be  called  basalt  por- 
phyry. In  the  less  porphyritic  form,  the  rock  is  very  compact, 
with  numerous  cavities  on  weathered  surfaces  which  doubtless 


32  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

mark  the  former  position  of  ferro-magnesian  minerals.  On  fresh- 
ly broken  surfaces,  these  do  not  appear,  but  many  small  patches 
of  limonite  attest  the  presence  of  pyroxene  in  the  original  rock. 

Idiomorphic  augite  crystals  with  a maximum  thickness  of 
.5  mm.  are  seen  under  the  microscope,  but  these  are  badly  altered. 
Numerous  prismatic  forms  with  the  extinction  angle  of  horn- 
blende occur,  but  they  are  too  badly  weathered  to  permit  certain 
identification.  Magnetite  is  abundant.  Serpentine  apparently  re- 
places small  olivine  crystals  and  occurs  throughout  the  slide  in 
company  with  chlorite.  Minute  lath-shaped  feldspars  compose 
less  than  half  the  rock.  Interstitial  augite  occurs  in  irregular 
grains,  and  minute  crystals  of  apatite  are  abundant. 

In  a short  dike  north  of  Sherwood  Creek  a porphyritic  basalt 
occurs,  in  which  the  feldspar  phenocrysts  far  outnumber  the 
augites.  This  rock  is  more  nearly  related  to  the  andesites  than 
are  the  other  basalts. 

Hornblende  basalts:  Two  varieties  of  hornblende  basalt  are 
present:  (1),  without  olivine  and  augite;  (2),  with  olivine  and 
augite.  The  first  occurs  in  a narrow  dike  a quarter  of  a mile 
south  of  the  old  Boulder  County  Mine.  It  is  dark  gray  with  very 
few  phenocrysts  of  feldspar  and  numerous  phenocrysts  of  what 
appears  to  be  hornblende. 

The  microscope  shows  that  the  hornblende  has  undergone 
complete  recrystallization.  The  mineral  is  replaced  by  aggre- 
gates of  minute  biotite  flakes  with  considerable  calcite,  magnetite 
and  a small  amount  of  quartz.  Inclusions  of  apatite  are  present. 
The  biotite  is  brownish-green  with  strong  pleochroism  and  high 
interference  colors.  The  feldspar  phenocrysts  are  too  badly  al- 
tered to  be  identified.  The  groundmass  is  composed  of  striated 
and  unstriated  feldspar,  small  flakes  of  biotite,  grains  of  mag- 
netite and  crystals  of  apatite,  with  secondary  quartz  and  calcite. 

The  second  variety  of  hornblende  basalt  is  found  in  a nar- 
row dike  south  of  Nederland,  crossing  the  old  Rollinsville  road. 
This  rock  contains  a multitude  of  hornblende  phenocrysts  with 
a few  augites  which  can  be  determined  in  the  hand  specimen. 
Most  of  the  phenocrysts  are  not  over  6 or  7 mm.  long,  but  a few 
reach  twice  that  length. 

The  hornblende  is  brownish-green  in  thin  section  and  extin- 
guishes at  about  15°.  Zonal  banding  is  very  marked.  The  augite 
is  almost  coloress  and  non-pleochroic.  The  crystals  have  ap- 
parently suffered  some  re-solution  and  are  bordered,  in  a few 
cases,  by  grains  of  augite,  variously  oriented.  A few  small  crys- 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


33 


tals  of  olivine  are  present,  but  are  mostly  replaced  by  serpentine. 
The  groundmass  is  composed  of  microlites  of  feldspar  and  augite 
with  small  grains  of  magnetite. 

Basalt  porphyry:  This  occurs  in  several  dikes,  but  the  fresh- 
est rock  is  exposed  at  the  railway  east  of  Rollinsville,  where  the 
dike  is  7 or  8 feet  wide.  The  rock  contains  abundant  phenocrysts 

01  augite  and  feldspar  in  a dense,  microcrystalline,  dark  gray 
groundmass.  The  augites  are  usually  less  than  5 mm.  long,  but 
a few  reach  a length  of  1 cm.  The  feldspars  are  usually  less  than 

2 mm.  in  diameter  and  are  bluish-gray  with  a vitreous  luster  in 
the  least  altered  rock.  They  become  white  and  more  conspicu- 
ous through  kaolinization.  The  groundmass  becomes  greenish  or 
light  gray  through  weathering,  or  on  sheltered  surfaces  often 
has  a reddish  cast. 

Under  the  microscope  the  rock  is  seen  to  be  holocrystalline, 
with  the  phenocrysts  composing  one-fourth  to  one-third  of  the 
rock.  The  augite  is  pale  green  and  slightly  pleochroic.  Olivine 
occurs  in  idiomorphic  crystals  1 mm.  long,  or  less.  These  pheno- 
crysts are  less  numerous  than  the  augites.  Alteration  to  serpen- 
tine is  common,  some  crystals  being  completely  replaced.  The 
feldspars  are  largely  basic  labradorite  or  bytownite,  and  probably 
exceed  the  augites  in  number.  The  groundmass  is  composed  of 
minute  feldspar  laths,  and  interstitial  magnetite,  pyroxene  and 
olivine.  Apatite  needles  are  abundant  as  inclusions. 

A much  coarser  textured  rock  occurs  in  the  dike  about  a 
quarter  of  a mile  south  of  Cardinal  Station.  In  this  rock  a few 
feldspars  reach  a diameter  of  1 cm.,  but  are  mostly  under  3 mm. 
The  pyroxene  phenocrysts  are  more  numerous.  Small  crystals  of 
pyrite  are  occasionally  present.  The  naked  eye  can  distinguish 
the  feldspar  grains  and  magnetite  of  the  groundmass.  In  addi- 
tion to  these  minerals,  the  microscope  shows  an  abundance;  of 
minute  apatite  crystals  and  flakes  of  chloritized  biotite  in  the 
groundmass,  besides  many  olivine  crystals  of  small  size.  The 
augite  is  invariably  uralitized. 

Pyroxenite. 

This  is  a greenish-gray,  even-grained  rock,  composed  almost 
entirely  of  pyroxene.  The  texture  varies,  but  is  always  sufficiently 
coarse  to  show  the  cleavage  surfaces,  which  sometimes  have  a 
sub-metallic  luster.  The  microscope  shows  the  presence  of  both 
monoclinic  and  orthorhombic  pyroxene,  and  perhaps  an  amphi- 


34 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


bole,  but  the  material  collected  is  too  unsatisfactory  for  furthei 
description. 

Limburgite. 

The  several  exposures  of  this  rock  are  probably  all  in  one 
dike,  which  is  so  narrow  that  it  does  not  reach  the  surface 
continuously  along  its  course.  The  width  ranges  from 
less  than  a foot  to  about  four  feet.  The  rock  is  almost  black, 
and  basaltic  in  appearance.  It  contains  abundant  grains  and 
pseudomorphs  of  serpentine  from  less  than  1 mm.  in  diameter 
to  3 or  4 mm.  Brown  mica,  in  occasional  small  crystals,  is  the 
only  primary  megascopic  constituent.  Amygdaloids  of  calcite 
are  common.  They  are  usually  less  than  1 cm.  in  diameter.  Frag- 
ments of  the  country  rock  usually  rounded  by  corrosion  are  very 
commonly  enclosed  by  the  dike.  These  inclusions  are  generally 
less  than  2 inches  in  diameter. 

The  microscope  shows  abundant  olivine,  which,  in  its  pheno- 
crystic  form  rarely  reaches  a diameter  of  5 or  6 mm.  Much  of 
the  olive  is  serpentinized,  and  green  chlorite  occasionally  ac- 
companies the  serpentine.  Olivine  in  smaller  crystals  and  grains, 
minute  prismatic  crystals  and  grains  of  augite,  grains  of  mag- 
netite and  multitudes  of  apatite  microlites  make  up  nearly  the 
entire  rock  mass.  These  occur  in  a colorless,  isotropic  base  which 
is  very  subordinate  in  amount. 

SURFACE  DEPOSITS. 

Glacial:  The  town  of  Nederland  is  just  within  the  glaciated 
area.  Glaciers  coming  down  from  the  crest  of  the  range,  in 
their  greatest  extension  down  Middle  Boulder  Creek,  passed  but 
a short  distance  beyond  Nederland.  The  source  of  all  the  mo- 
rainal deposits  of  the  region  is  to  the  westward,  northwestward, 
and  perhaps  a little  to  the  southwestward.  It  is  not  unlikely 
that  the  main  ice  streams  of  South  Boulder,  Middle  Boulder  and 
North  Boulder  Canyons  may  have  coalesced  on  the  lower  portions 
of  the  divide,  as  morainal  matter  is  found  at  high  points  adja- 
cent to  the  canyons.  Little  is  yet  known  as  to  distinct  periods 
of  extension  and  retreat  of  the  glaciers  of  the  region,  but  what- 
ever fluctuations  there  may  have  been,  the  general  movement  of 
the  ice  was  probably  always  from  west  to  east,  though  varying 
a few  degrees  locally.  Hence  it  is  safe  to  say  that  all  the  ma- 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


35 


terial  of  the  various  moraines  has  in  a general  way  come  from 
a westerly  direction.  The  drift  is  without  doubt  chiefly  Pleisto- 
cene, but  inasmuch  as  moraines  are  now  forming  at  the  foot  of 
Arapahoe  Glacier,  those  in  the  west  part  of  the  area  under  con- 
sideration should  perhaps  be  considered  in  part  Recent. 

The  drift  material  is  a mixture  of  glacial  clay  and  boulders, 
which  include  gneiss,  granite  and  porphyries,  some  of  which  are 
not  represented  in  the  unglaciated  area  toward  the  east.  The 
boulders  range  in  size  from  mere  pebbles  to  masses  several  feet 
in  diameter.  Angular  forms  are  sometimes  present,  but  the  boul- 
ders are  commonly  more  or  less  rounded  as  the  result  of  a roll- 
ing, grinding  movement.  Such  faceting  as  occurs  is  usually 
obscure,  and  the  character  of  the  material  leads  to  rapid  weath- 
ering, so  that  any  polishing  and  striation  that  may  have  been 
originally  present  have  been  destroyed  on  all  material  examined. 

Alluvial:  In  the  western  part  of  the  area  where  streams 
have  only  a moderate  gradient,  North,  Middle  and  South  Boul- 
der Creeks  have  locally  accumulated  a considerable  depth  of  allu- 
vium. Gold  placers  were  formerly  worked  in  South  Boulder  at 
Pactolus  and  near  the  mouth  of  Winiger  Creek.  In  the  meadows 
in  Middle  Boulder  Creek,  about  two  miles  above  Nederland,  the 
alluvium  is  largely  of  lacustrine  origin,  doubtless  deposited  in  a 
glacial  lake  which  has  since  been  drained  by  a lowering  of  the 
outlet.  The  alluvium  of  the  Barker  Meadows  just  east  of  Neder- 
land was  also  deposited  in  a lake  formed  by  the  damming  of  the 
channel,  probably  by  stream-carried  glacial  debris  at  the  dam 
site  of  the  Eastern  Colorado  Power  Company. 

Exposed  rock  surfaces  gradually  become  covered  by  a thin 
layer  of  mineral  grains  and  rock  fragments  of  various  sizes, 
which  have  been  loosened  from  the  parent  mass  in  the  ordinary 
processes  of  weathering.  By  further  decay  of  this  detritus  a 
matrix  of  clay  and  fine  rock  grains  fills  the  spaces  between  the 
fragments.  Heavy  showers,  forming  temporary  streams  and 
sheets  of  water,  sweep  this  material  from  the  steep  mountain  and 
hill  sides  to  the  gentler  slopes  of  the  valley,  where  the  stream 
loses  its  force,  spreads  over  the  surface  or  sinks  into  the  ground, 
and  its  load  of  detritus  is  left  stranded.  Such  deposits  of  sheet- 
wash  or  slope-wash  are  formed  most  rapidly  where  small,  steep 
ravines  join  the  larger  valley  with  its  gentler  slopes.  If  these 


36 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


small  ravines  or  notches  are  numerous,  these  deposits  may  spread 
until  their  edges  unite  and  the  gentler  slopes  of  the  larger  valley 
may  be  deeply  buried  by  a continuous  sheeu  Sucii  sneets  of 
slope-wash  occur  locally  along  all  the  main  streams  of  the  tung- 
sten area.  The  more  prominent  examples  of  this  kind  are  on 
the  north  side  of  Beaver  Creek,  near  Pactolus  on  South  Boulder, 
and  east  and  west  of  Nederland  on  Middle  Boulder. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


37 


CHAPTER  II.— ECONOMIC  GEOLOGY. 


TUNGSTEN  MINERALS. 

The  tungsten  of  commerce  is  obtained  almost  exclusively 
from  the  four  minerals:  wolframite,  ferberite,  hubnerite  and 
scheelite. 

Hubnerite  is  theoretically  a tungstate  of  manganese,  Mn 
W04,  but  iron  generally  replaces  a small  part  of  the  manganese. 
The  average  of  eleven  analyses  of  hubnerite  gives  the  following 
percentage  composition : 


WOg  (tungstic  oxide) 75.23 

FeO  (ferrous  oxide) 2.11 

MnO  (manganous  oxide) 23.07 


Well-formed  crystals  of  hubnerite  are  very  rare,  but  forms 
with  two  or  three  crystal  faces  are  somewhat  common.  The 
mineral  shows  a tendency  to  form  groups  of  bladed,  prismatic, 
and  needle-like  crystals  in  which  the  individuals  are  frequently 
divergent.  Thin  tabular  forms  occur  alone,  and  in  lamellar 
masses.  Compact,  granular  ore  is  common.  The  cleavage  is 
perfect.  The  color  of  the  crystal  faces  is  usually  dark  brown  to 
black;  but  the  flat,  very  smooth  or  splintery  cleavage  faces  are 
commonly  reddish  brown  to  hair-brown,  and  sometimes  black. 
It  is  easily  scratched  with  a knife,  and  the  powder  formed  shows 
lighter  shades  of  brown  than  the  surface  from  which  it  comes. 
(The  water-made  concentrates  from  some  of  the  San  Juan  ores 
of  Colorado  are  very  dark — almost  bluish  black.)  The  luster 
of  crystal  surfaces  is  bright  submetallic,  while  that  of  cleavage 
and  fracture  surfaces  is  submetallic  to  resinous.  The  specific 
gravity  is  7.2  to  7.5,  or  about  three  times  that  of  quartz  or 
granite.  The  fusibility  depends  upon  the  purity.  Thin  splinters 
of  the  pure  mineral  are  readily  fused  before  the  blowpipe,  and 
small  grains  will  fuse  rather  readily  in  the  forge.  If  quartz  is 
intimately  mingled  with  the  mineral,  as  is  frequently  the  case,  it 
becomes  difficultly  fusible,  and  sometimes  almost  infusible  before 
the  blowpipe. 

Wolframite  is  an  iron-manganese  tungstate  in  which  the  ra- 
tio of  iron  to  manganese  may  range  from  9:1  to  2 :3.  This  varia- 


38 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


tion  in  the  ratio  of  two  of  the  three  metallic  elements  results 
in  a varying  percentage  of  each  of  the  metallic  oxides  com- 
posing the  mineral.  With  the  increase  of  the  iron  percentage, 
it  approaches  ferberite,  and  with  the  increase  of  manganese  it 
becomes  more  like  hubnerite.  The  average  of  about  20  analyses 
gives  the  following  result: 


W03  (tungstic  oxide) 76.0% 

FeO  (ferrous  oxide) 16.0% 

MnO  (manganous  oxide) 7.7% 


With  some  modifications,  the  description  of  hubnerite  would 
apply  to  wolframite.  The  color  is  dark  brown  to  black,  and 
sometimes  dark  steel  gray.  The  powder  and  streak  are  gen- 
erally dark-brownish  black,  but  may  be  black  or  grayish 
black.  The  luster  of  cleavage  surfaces  is  fairly  bright  sub- 
metallic.  The  cleavage  of  crystals  is  good  and  causes  them  to 
break  into  plates.  As  an  ore  it  is  commonly  massive  granular, 
but  druses  or  crusts  of  ore  frequently  show  enough  crystal  faces 
to  make  out  prismatic  and  chisel-shaped  forms.  The  granular 
aggregates  are  likely  to  part  between  the  crystal  grains  and 
show  comparatively  few  cleavage  faces,  while  the  broken  or 
bruised  surfaces  of  druses  will  show  many  cleavage  planes  which 
may  be  mistaken  for  crystal  faces. 

Scheelite  is  a calcium  tungstate,  CaW04,  with  W03  80.6% 
and  CaO  19.4%.  Molybdenum  may  replace  part  of  the  tungsten. 
In  color  it  varies  from  colorless  and  transparent  to  honey-yel- 
low, greenish  yellow,  to  rusty  brown,  pink  and  reddish.  Crystals 
are  frequently  found  on  the  walls  of  cavities.  Four-sided  pyra- 
mids and  octahedral  forms  are  commonest.  Tabular  forms  and 
forms  described  under  wolframite  and  ferberite  are  found — the 
latter  are  pseudomorphs  after  wolframite  or  ferberite.  The 
luster  of  crystal  faces  is  vitreous  to  adamantine,  while  that  of 
fractures  and  cleavage  faces  is  less  brilliant,  and  inclines,  at 
times,  to  resinous  and  greasy.  The  mineral  is  often  coarsely 
granular,  with  cleavage  faces  fairly  prominent  on  the  broken 
surface  of  the  mass.  It  is  rather  easily  scratched  with  a knife, 
has  a specific  gravity  of  6,  or  a little  more  than  double  that  of 
quartz.  It  is  readily  soluble  in  nitric  and  hydrochloric  (muriatic) 
acid,  with  the  formation  of  a yellow  powder,  tungsten- 
trioxide,  which  is  soluble  in  ammonia.  (Pour  off  excess  of  acid, 
leaving  yellow  powder  behind.  Add  ammonia  liberally.)  The 
yellow  powder  treated  with  zinc  or  tin  in  the  acid  solution  is 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


39 


reduced  to  a lower  oxide  form  having  a beautiful  blue  color, 
changing  slowly  through  wine  color  and  purple  to  brown. 

Minerals  which  resemble  scheelite  are:  quartz,  barite  (ba- 
rium sulphate),  witherite  (barium  carbonate),  anglesite  (lead 
sulphate),  and  cerussite  (lead  carbonate).  The  following  table 
gives  the  distinguishing  features  of  these  minerals  and  scheelite : 


40 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY 


G 

c 

1 

© 

© 

© 

© 

© 

© 

> 

> 

' 

G 

G 

G> 

to 

be 

© 

© j 

® .2 

« g 

© 

G 

O 

© 

o 

fa 

CO 

CO 

C 

fa> 

CO 

G I 

CO 

fa3 

7< 

'% 

£ 

3 

'G 

o 

o 

© 

© 

o 

£ 

s 1 

be 

© 

B o B 

3g£ 

© 

fa 

c-2 

.5  fa 

3 

3fc* 

° 3-3 

© 

3 

G 

O 

3 . > 

_ © 

tj  fa  « 

3 

33 

3 G 

— © T 

fa  2 

3 o 

O +j 

fe 

CO 

o 

CO 

32 

©.2 

G 

3c 

Solu 
hyd 
and  n 

W O O 
d fa  _ 

M © 

.2 

“ 

G 

o ds 

CO  >» 
fa 

ItG  -*-* 

S'c 

fa 

o 

CO 

0) 

m 

dJ 

.So 

© 

£ 

- G 

3 co  c\j 

G © 
d fa 

a;  o5 

© 

>rH 

m! 

£ ads  © 

«■ 

>>*B 

a G O- 

"m 

CO 

3 

eas 

d W.2 
© 'd  © 

>>3 
fa  ®d 
w £ d 

fa  o £ 

33 

G fa 

d ^ © 

5 o 
co  © 3 

3 to 

fa 

G 

© 

fa 

-*-> 

d 

G 

Easilj 

Very 

Very 
oils  a 

and 

metal 

ery  e 

gives 

1 

fa 

fa 

f> 

_L  fa  d 

3 c 

0) 

o 

<D 

G 

© 

G O, 

gd 

h » 

Sri 

> 

G 

'■age — 

to 

smoot 

faces. 

O 

— ' © 

© 

None. 

g-2 

,rH  © 

® 

5 

o 

G 5 
— 1 © 

© 

G G 

fair; 

brittle 

d 

O 

£ 

d ©fa 
®G.fa 

d 3 
fa 

O ^3 

O 

d 3 
fa 

£ 

EH 

O « £ 

EH 

a red  i 

vol- 

nite 

as 

© 

© 

o 

© . 

1 g* 

>.fa 

t comp 
equal 
of  gra 
quartz 

twice 

leavy. 

B 

d 

© 

>> 

G co 
o © 

«J 

G *J 

co  © 
d -m 

© © 

S 2 

|1 

^fa 

© 

3* m 

fa  g 

bofa  © o 

Sh  ^ 

a; 

> 

© 

© 3 
g si 

® w 

fa  G 
be  d 

©3  H 

0 

3^ 

o 

fa^= 

£ £ 3 

CO  ^ 

' 

© 

1 

© 

o 5 © 

fa 

© 

CO 

© 

. 

fa  d5 

fa  di 

£ d 

T3 

S'  ® ® 

U3  d 

co  © 

CO  © 

© © 

• d fa 

t—  G 

d fa 

d fa 

Hardness 
pared 
knife  b 

r*  <4-‘ 

© G 

© 

m 

Scratches 

(2.5-3 
Very  e 
scratc 

(3.-3.1 
Easily  sc 

h 

Very  e 
Scratc 

Very  e, 
Scratc 

© 

© 

fa 

2 

© 

© 

fa 

© 

CO 

Quartz 

Barite . 

’g 

© 

Si 

> 

to 

© 

3) 

G 

i <3 

M I 

§ 

G 

© 

o 

MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


41 


Ferberite : The  name  was  first  applied  to  an  iron-manganese 
tungstate  from  the  Sierra  Almagrera,  Spain,  which  contained  3.0 
per  cent,  of  MnO.  The  view  that  the  name  should  be  reserved  for 
a practically  pure  ferrous  tungstate  seems  to  be  somewhat  prev- 
alent, but  the  example  above,  and  the  common  usage  in  regard 
to  other  minerals,  do  not  justify  this  restriction.  Dana  does  not 
mention  any  crystallographic  difference  between  ferberite  and 
wolframite  greater  than  that  recorded  between  different  hubnerite 
crystals.  Reinite  (34,  p.  991)  is  a pure  ferrous  tungstate  from 
Japan,  but  the  crystals  are  probably  pseudomorphs  after  schee- 
lite.  A “wolframite”  from  the  Black  Hills  (34  “Appendix,”  p. 
73),  is  said  to  show  no  reaction  for  manganese,  and  is  “inferred 
to  be  the  pure  iron  tungstate.”  The  crystal  angles  correspond 
closely  with  those  of  ordinary  wolframite.  In  speaking  of  ar- 
tificial ferrous  tungstate,  Dana  says  (34,  p.  985)  : “A  little  man- 
ganese is  also  present.”  The  following  analyses  of  ores  from  the 
Nederland-Beaver  Creek  part  of  the  field  show  a very  small  per- 
centage of  manganese,  and  when  the  parts  not  essential  to  the 
mineral  are  eliminated,  the  remainders  show  an  excess  of  fer- 
rous oxide  over  that  required  to  make  the  ferrous  tungstate, 
FeW04.  Magnetite  is  present  in  small  amount  in  most  of  the 
ores  and  in  some  of  the  gangue  material,  but  the  ferric  iron  was 
not  worked  out,  and  therefore  the  extent  to  which  this  excess  of 
iron  would  be  reduced  by  eliminating  the  magnetite  cannot  be 
determined.  A few  inexact  tests  of  Nederland  ores  show  from 
.5  to  1.2  per  cent,  of  magnetite.  Dana  suggests  that  the  ferberite 
molecule  may  be  n FeW04.FeO.  This  would  take  care  of  the 
excess  of  FeO. 

The  manganous  oxide,  MnO,  of  the  complete  ore  analyses 
averages  0.5  per  cent.,  and  that  of  the  same  analyses  after  the 
non-essentials  are  removed  averages  0.56.  (Similar  results  arfc 
shown  by  the  partial  analyses  of  ores  and  concentrates  from 
the  same  part  of  the  field.)  If,  as  suggested  by  Roscoe  and  Schor- 
lemmer  (98,  p.  1058),  the  MnO  is  taken  with  the  FeO  the  com- 
position would  be  n FeW04.  (FeMn)  O.  In  the  Nederland-Beaver 
Creek  ores  the  value  of  n would  range  from  3 to  21.  Comparing 
these  with  Dana’s  analyses  of  ferberite,  it  is  evident  that  they  are 
much  more  nearly  pure  ferrous  tungstates  than  was  the  original 
ferberite.  Dana  also  says  (34,  p.  983) , “Hubnerite  is  nearly  pure 
MnW04.”  But  the  ten  analyses  given  (34,  p.  984)  all  contain 
FeO,  and  the  average  percentage  is  2.11.  These  ferberites  are 


42 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


therefore  more  nearly  pure  ferrous  tungstates  than  are  Dana’s 
hubnerites  pure  manganese  tungstates. 


Analyses  of  Ferberite  from  the  Nederland-Beaver  Creek 
area: 

W03  FeO  MnO  CaO  Si02  A1203  MgO 

Clyde  Mine 61.15  19.33  0.51  0.38  16.10  2. 49*  0.39 

Barker  Ranch 65.88  24.14  0.37  0.35  6.45  2.19  0.50 

Conger  Mine 60.98  19.13  0.08  0.44  15.94  3.10  0.59 

Last  Chance 62.30  19.90  0.69  0.79  14.68  1.34  ___ 

Magnolia  73.94  23.85  0.67  0.60  0.49  0.25  0.12 

Elsie  73.52  22.65  0.60  0.42  1.81  0.75  

Manchester  Lake 74.13  23.15  0.56  1.28  0.71  0.46  


As  scheelite  is  present  in  many  of  the  mines,  it  is  probable 
that  most  of  the  CaO  comes  from  that  mineral.  A small  part 
may  come  from  the  feldspar  of  the  gangue,  but  as  plagioclase 
is  rather  rare,  in  the  rock  fragments,  the  quantity  of  CaO  from 
this  source  may  be  neglected.  Assuming  that  the  CaO  is  from 
the  scheelite,  and  deducting  enough  tungstic  oxide  to  satisfy  it, 
and  eliminating  the  silica,  alumina  and  magnesia  as  non-essen- 
tials, the  analyses  in  the  first  group,  reduced  to  a basis  of  one 


hundred  per  cent.,  would  read: 

Excess  of 

W°3 

FeO 

MnO 

FeO 

Clyde  Mine 

75.28 

24.43 

0.64 

1.06 

Barker  Ranch 

72.36 

27.11 

0.42 

4.65 

Conger  Mine 

75.68 

24.47 

0.10 

0.99 

Last  Chance 

73.92 

24.92 

0.86 

1.99 

Magnolia  _ _ _ — 

74.58 

24.90 

0.70 

1.75 

Elsie  _ 

75.35 

23.76 

0.60 

0.38 

Manchester  Lake — 

74.57 

25.12 

0.61 

1.98 

^Partial  analyses  of  Nederland  ores : 

w°3 

MnO 

39.82 

0.53 

35.12 

0.38 

41.52 

0.52 

50.20 

0.56 

20.52 

0.30 

21.00 

0.31 

64.90 

0.93 

•Assays  by  H.  F.  Watts,  Boulder, 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


43 


^Partial  analyses  of  Nederland  concentrates  : 


W°3 

MnO 

60.432 

0.64 

52.30 

0.38 

61.10 

0.69 

62.49 

0.50 

63.21 

0.64 

61.50 

0.66 

Analyses  of  ores  from  the  northeastern  area:  The  follow- 
ing three  analyses  are  of  ores  from  the  northeastern  area. 
These,  and  assay  returns  from  both  ores  and  concentrates,  show 
higher  percentages  of  manganous  oxide  for  this  part  of  the  field. 
A large  number  of  assays  and  analyses  made  by  the  Colorado 
Tungsten  Corporation  at  the  Boyd  Mill  show  an  average  of  3 
per  cent,  manganous  oxide,  MnO. 


wo3 

FeO 

MnO 

CaO 

SiO 

A1  O 

9 ^ 

MgO 

Boulder 

Falls 

70.42 

19.85 

3.36 

2.87 

2.37 

6 O 

1.26 



Hal  Harlow 

55.05 

17.69 

1.47 

3.05 

19.23 

3.70 



Gordon 

Gulch 

61.80 

16.36 

3.12 

0.35 

15.93 

1.06 

1.71 

After  satisfying  the  CaO  with  W03  (to  form  scheelite),  and 
eliminating  the  silica,  alumina  and  magnesia,  the  following  re- 
sults are  obtained  by  reducing  the  remainders  to  the  basis  of  100 


per  cent.: 


W°3 

FeO 

Boulder  Falls  _ 

. . 71.70 

24.32 

Hal  Harlow  _ _ 

69.02 

28.78 

Gordon  Gulch 

. _ 75.85 

20.56 

MnO 

4.16 

2.39 

3.92 


By  treating  Dana’s  ferberite  analyses  (34,  p.  985),  in  the 
same  way,  it  is  found  that  the  ratio  of  MnO  to  W03  is  practically 
the  same  as  in  these  three.  The  average  percentage  of  manganous 
oxide  for  the  ten  analyses  above  is  1.44,  while  the  lowest  per- 
centage given  in  Dana’s  analyses  of  wolframite  is  2.37  and  the 
average  is  7.66  (34,  p.  984). 

The  following  are  analyses  of  tungsten  minerals  from  other 
parts  of  the  State: 

Wolframite: 


wo3 

FeO 

MnO 

CaO 

SiO  A1  O 

2 2 3 

ISultan  Mountain,  near  Sil- 

verton 

74.09 

11.07 

14.35 



0.43  

Johnnie  Ward  Mine,  Ward. 

71.27 

20.01 

7.15 

1.58 



♦Assays  by  H.  F.  Watts,  Boulder. 

1 From  Dana’s  System  of  Mineralogy,  page  984. 


44  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Hubnerite: 


wo 

FeO 

MnO 

CaO 

Si°2 

A1  O 

Natalie  Mine,  Gladstone 

70.21 

2.03 

21.72 

0.37 

4.91 

0?56 

iN.  Star  Mine,  Silverton 

74.75 

2.91 

21.93 

0.11 





iCement  Creek,  Silverton 

76.63 

1.61 

21.78 

0.09 





iQuray  County  _ _ 

75.58 

0.24 

23.40 

0.13 





The  ferberite  is  generally  almost  black, 

with  a 

slight  ten 

dency  to  brownish  black,  and  on  fresh  granular  surfaces  a weak 
steel  gray  color.  The  luster  varies  with  the  surface  examined. 
Natural  crystal  surfaces  are  usually  submetallic  to  dull  sub- 
metallic,  while  cleavage  surfaces  are  brilliant  submetallic,  often 
rivaling  black  mica  in  brightness.  The  fresh  surfaces  of  the 
massive,  granular  mineral  frequently  show  a rather  high  sub- 
metallic luster.  The  cleavage  is  perfect,  and  the  mineral  shows 
a tendency  to  break  into  thin  crumbling  plates.  Small  crystals 
are  common  in  cavities.  The  prevailing  forms  are  thick,  chisel- 
shaped, having  two  curved,  and  generally  striated,  faces,  converg- 
ing to  form  the  cutting  edge  of  the  chisel.  The  other  two  faces 
are  parallel,  and  approximately  at  right  angles  to  the  cutting 
edge.  Lance  or  spear-head  crystals  are  also  rather  common — 
the  longer  diameter  of  the  cross  section  of  the  spear-head  being 
double  the  shorter.  Loose  bunches  of  lath-shaped  and  slender 
prismatic  crystals  are  found.  These  crystals  commonly  lie  with 
their  longer  dimensions  parallel  to  the  surface  to  which  they  are 
attached.  The  great  bulk  of  the  ore  is  very  fine,  massive  granu- 
lar. The  specific  gravity  ranges  from  7.1  to  7.5  (nearly  three 
times  that  of  quartz) . The  streak  made  on  a light  colored,  hard 
surface,  or  on  rough  porcelain,  is  dark  grayish  black,  with  a sug- 
gestion of  brown.  The  powder  made  by  scratching  the  surface 
with  a knife  is  black  to  very  dark  brownish  black. 

The  fusibility  varies  with  the  purity.  The  pure  mineral,  in 
thin  splinters,  is  rounded  and  fused  with  no  great  difficulty,  but 
the  siliceous  granular  ore  is  nearly  infusible.  The  fusibility 
seems  to  vary  with  the  percentage  of  manganese  present.  Even 
pure  crystal  fragments  of  the  ore  almost  free  from  manganese 
are  difficultly  fusible,  and  the  siliceous  ore  of  the  same  composi- 
tion remains  practically  unchanged  before  the  blowpipe. 

Minerals  resembling  the  dark  tungsten  ores:  Minerals  which 
may  be  mistaken  for  wolframite,  ferberite  and  hubnerite  are: 
magnetite  and  hematite  (iron  oxides)  ; limonite,  goethite  and 
turgite  (hydrous  oxides  of  iron)  ; ilmenite  (iron-titanium  oxide)  ; 


1 From  Dana’s  System  of  Mineralogy,  page  984. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


45 


psilomelane,  manganite  (hydrous  oxides  of  manganese)  ; pyrolu- 
site  (oxide  of  manganese)  ; rutile  (titanium  oxide)  ; cassiterite 
(tinstone,  tin  oxide)  ; tourmaline  (a  complex  silicate  of  boron, 
aluminum,  etc.).  All  of  these  but  manganite,  ilmenite  and  tour- 
maline are  infusible.  Manganite  and  ilmenite  are  nearly  infus- 
ible, and  black  tourmaline  is  very  difficultly  fusible.  In  specific 
gravity,  all  except  cassiterite  are  far  below  the  tungsten  minerals. 
The  heaviest,  hematite  and  magnetite,  are  about  twice  as  heavy, 
volume  for  volume,  as  granite,  while  tourmaline  is  only  slightly 
heavier  than  granite.  The  tungsten  minerals  are  nearly  or  quite 
three  times  as  heavy  as  granite.  The  three  tungsten  minerals 
have  very  perfect  cleavage.  Only  manganite,  turgite  (and  rutile) 
resemble  them  in  this  respect.  Manganite  and  pyrolusite  are 
quite  soft,  while  rutile,  cassiterite  and  tourmaline  are  harder 
than  the  tungsten  ores  and  can  scarcely  be  scratched  with  a knife. 
The  others  have  about  the  same  hardness  as  the  dark  tungsten 
ores.  All  but  rutile  and  tourmaline  are  soluble  in  hydrochloric 
acid  (cassiterite  nearly  insoluble),  but  only  ilmenite  gives  a yel- 
low solution.  The  yellow  color  of  the  tungsten  solution  is  due  to 
the  formation  of  yellow  tungstic  oxide,  which  soon  settles  to  the 
bottom  after  boiling  ceases,  while  that  of  the  ilmenite  solution  is  a 
true  coloration.  The  tungsten  minerals  are  much  more  brittle  and 
easily  powdered  than  are  the  iron  ores,  ilmenite,  and  cassiterite 
and  tourmaline. 

A number  of  other  minerals  bearing  tungsten  are  known, 
but  they  have  not  yet  been  found  in  commercial  quantities.  The 
names  and  compositions  of  a few  are  as  follows : 

Reinite — a ferrous  tungstate,  FeW04 — possibly  a pseudo- 
morph  after  scheelite  ; stolzite — a lead  tungstate,  PbW04; 
raspite — a lead  tungstate;  cuprotungstite — a copper  tungstate, 
CuW04;  cuproscheelite — a tungstate  of  calcium  and  copper,  (Ca, 
Cu)W04;  tungstite  (and  meymacite) — hydrous  tungstic  oxide, 
W08.  H20,  (119). 

TESTS  FOR  TUNGSTEN. 

1.  Completely  pulverize  the  mineral,  place  a small  quantity 
in  a test-tube  with  hydrochloric  acid.  Boil  vigorously  for  fif- 
teen or  twenty  minutes  if  hubnerite,  ferberite  or  wolframite  is 
looked  for,  or  about  ten  minutes  if  scheelite  is  expected.  A fine 
yellow  powder,  tungstic  oxide,  W03,  is  formed.  When  a small 
piece  of  tin  or  zinc  is  added,  the  yellow  powder  and  the  pow- 


46  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

dered  tungsten  mineral  are  changed  to  a fine  blue.  The  tungstic 
oxide  is  reduced  by  the  stannous  chloride  to  a lower  hydrous 
oxide,  W5014.  H20,  (1).  If  concentrated  or  very  strong  hydro- 
chloric acid  is  used  the  blue  solution  will  soon  change  through 
wine  color  to  purple-brown,  and  finally  to  brown.  If  dilute  acid 
is  used  the  blue  color  will  last  much  longer.  Dilute  sulphuric 
acid  may  be  used,  but  in  the  case  of  the  dark  tungsten  ores, 
requires  a longer  time  to  produce  the  tungstic  oxide.  The  blue 
color  obtained  by  reducing  with  zinc  or  tin  is  more  lasting  than 
that  obtained  by  treating  with  strong  hydrochloric  acid.  If  the 
finely  powdered  mineral  is  fused  with  ten  to  fifteen  times  its 
volume  of  sodium  carbonate  (or  baking  soda)  in  an  iron  spoon, 
and  then  dissolved  in  acid  and  treated  with  the  zinc  or  tin,  the 
results  will  be  the  same,  but  the  test  will  be  more  certain,  since 
the  minerals  are  rather  hard  to  break  up  with  the  acids  alone. 

The  powdered  mineral  is  more  readily  dissolved  in  aqua  regia 
(nitric  acid  one  part,  hydrochloric  acid  uiree  parts). 

2.  A test  which  has  proved  satisfactory  with  the  dark  tung- 
sten ores  may  be  made  as  follows:  Reduce  the  mineral  to  a 
very  fine  powder  and  fuse  with  sodium  carbonate  (baking  soda) . 
Dissolve  the  mass  by  boiling  in  water,  add  a few  grains  of  am- 
monium sulphocyanate,  and  heat  gently  to  dissolve  the  salt.  Add 
dilute  hydrochloric  acid.  A bright  wine-red  is  produced.  Add 
tin  and  boil.  The  red  disappears  and  is  followed  after  a short  time 
by  a rich-green  solution.  The  depth  of  the  green  will  depend 
upon  the  strength  of  the  solution. 

3.  Follow  the  first  test  until  the  first  boiling  has  occupied 
twelve  or  fifteen  minutes,  then  add  a little  nitric  acid  and  boil 
about  five  minutes.  Allow  the  yellow  powder  to  fall  to  the  bot- 
tom, and  drain  off  the  liquid.  Add  ammonia.  If  the  yellow 
powder  is  dissolved,  it  was  formed  by  tungsten.  The  ammonia 
solution  may  be  acidified  with  hydrochloric  acid  and  tin  added. 
The  blue  color  produced  by  boiling  will  not  disappear  when  the 
solution  is  diluted  with  water. 

4.  The  salt  of  phosphorous  bead  containing  a little  tungstic 
oxide  is  colorless  in  the  oxidizing  flame,  but  blue  in  the  reducing 
flame. 

OCCURRENCE  OF  TUNGSTEN  MINERALS. 

The  modes  of  occurrence  of  the  various  tungsten  minerals 
can  best  be  understood  by  reference  to  typical  deposits. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


47 


Scheelite : In  the  Cariboo  district  near  Barkerville,  B.  C., 
a white  to  buff-colored  scheelite  of  rather  coarse  granular  habit 
accompanies  galena,  pyrite  and  siderite  in  quartz  stringers  in 
a zone  from  twelve  to  twenty  feet  wide  in  a highly  altered  mica 
schist.  The  scheelite,  is  semi-transparent  to  opaque,  shows  dis- 
tinct cleavage  faces,  and  has  a dull,  almost  earthy  luster.  The 
scheelite  at  Nome,  Alaska,  is  in  a similar  country  rock. 

In  the  Victorio  district,  near  Deming,  N.  M.,  scheelite  oc- 
curs with  pyrite,  lead  minerals  and  hubnerite  in  a vein  cutting 
limestone. 

Contact  deposit  at  Trumbull,  Conn.:  Scheelite  occurs  at 
the  contacts  of  a limestone  and  a hornblende  gneiss,  where  it 
is  associated  with  quartz,  zoisite,  garnet,  epidote  and  other  min- 
erals characteristic  of  contact  metamorphism.  The  scheelite  oc- 
curs mainly  in  the  upper  part  of  the  hornblende  gneiss,  just  be- 
low the  lower  contact  plane,  where  it  is  irregularly  distributed 
ir  grains,  crystals,  and  aggregates  as  large  as  the  fist,  and 
forms  5 per  cent,  of  the  vein.  Wolframite  derived  from  the 
scheelite  is  also  present. 

In  La  Sorpresa  mine,  Spain,  scheelite  and  wolframite  oc- 
cur in  white  quartz  at  the  contact  of  Cambrian  slates  and 
granite. 

As  a gangue  mineral : In  the  eastern  part  of  Missoula  Co., 
Mont.,  scheelite  forms  the  gangue  or  vein  matter  of  a gold  de- 
posit. Near  Jardine,  Park  Co.,  Mont.,  scheelite  occurs  in  bluish 
white  quartz.  Near  Caliente,  Kern  Co.,  Cal.,  a rich  ledge  of 
scheelite  occurs  in  a lead-silver  mine. 

Scheelite  occurs  in  a number  of  placer  deposits,  as  at  Nome, 
Alaska,  but  the  mineral  is  derived  from  nearby  vein  deposits. 

Near  Hill  Grove,  in  New  South  Wales,  scheelite  occurs  in 
numerous  veins  in  a gneissic  granite.  In  New  Zealand,  scheelite 
occurs  in  the  auriferous  quartz  reefs  of  Otago  and  Marlborough. 
In  Marlow  township,  Beauce  Co.,  Quebec,  scheelite  occurs  in 
association  with  specular  iron,  pyrrhotite,  galena,  chalcopyrite, 
pyrite,  in  quartz  veins  cutting  Cambrian  slates.  Tungstite  (or 
meymacite)  sometimes  accompanies  the  scheelite. 

Scheelite  in  small  quantity  has  been  found  associated  with 
pyrrhotite,  chalcopyrite,  pyrite,  pentlandite  and  various  other 
rare  minerals  in  the  Victoria  mine  (nickel,  Sudbury,  Ontario). 
The  country  rock  of  the  nickel  deposits  is  norite. 


48 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Scheelite  and  other  tungsten  minerals  are  associated  with 
tin  ores  in  many  tin-mining  regions,  such  as  England,  Bolivia, 
Queensland,  New  South  Wales,  East  Indies,  Australia,  Spain, 
Portugal,  and  Germany.  In  a number  of  these  the  country  rock 
is  greisen.  Other  minerals  with  which  scheelite  may  be  found 
are  topaz,  fluorite,  apatite,  molybdenite  and  antimony. 

Wolframite  and  hubnerite : The  Black  Hills  wolframite  oc- 
curs in  flat,  horizontal,  but  rather  irregular  masses,  intimately 
associated  with  the  oxidized,  refractory  siliceous  ores  formed 
by  the  replacement  of  a magnesian  limestone  by  uprising  solu- 
tions along  fracture  lines  passing  from  the  underlying  pre-Cam- 
brian rocks  up  into  the  limestone.  Before  oxidation,  the  ore 
carried  pyrite,  fluorite,  barite  and  occasionally  gypsum.  In  the 
Tungsten  Mining  District  southeast  of  Ely,  Nevada,  hubnerite 
in  fine  grains,  with  a little  fluorite,  pyrite  and  scheelite,  occurs 
ii  compact  quartz  forming  a branching  system  of  veins  cutting 
a granite  porphyry  intruding  Cambrian  quartzites  and  argillites. 
Wolframite  occurs  as  a pseudomorph  (replacement  retaining  the 
same  crystal  form)  after  scheelite  in  the  Trumbull,  Conn.,  de- 
posit mentioned  above.  At  Nigger  Hill  and  Etta  tin  mines,  in 
the  northwestern  Black  Hills,  wolframite  is  found  in  the  pre- 
Cambrian  rocks  as  a constituent  of  pegmatitic  granites  of  the 
greisen  type.  In  Beira  Baixa  province,  Portugal,  wolframite 
occurs  with  cassiterite,  oxide  of  iron,  pyrite,  arsenopyrite  and 
mica  in  a quartz  gangue  in  schists  of  Cambrian  age. 

In  northern  Queensland  wolframite  deposits  occur  in  gran- 
ite, greisen,  felsite,  quartz-porphyry,  chlorite  schist,  slate  and 
quartzite.  The  gangue  materials  are  almost  as  varied — includ- 
ing quartz,  chlorite,  muscovite,  biotite,  topaz  rock,  fluorspar, 
beryl-rock  and  greisen  with  and  without  quartz.  The  common- 
est country  rock  is  granite  and  the  commonest  gangue  is  quartz. 
With  the  wolframite  are  also  associated  bismuth  in  several 
forms,  molybdenite  and  minerals  bearing  manganese,  tin,  iron, 
copper,  lead,  zinc,  uranium  and  cerium. 

In  the  North  Star  mine,  Silverton,  Colorado,  hubnerite,  as- 
sociated with  fluorite,  occurs  in  a quartz  gangue  carrying  auri- 
ferous pyrite,  argentiferous  galena,  tetrahedrite,  chalcopyrite, 
sphalerite  and  barite.  The  fluorite  and  hubnerite  are  later  than 
the  main  vein  filling.  The  country  rock  is  a quartz  monzonite. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  49 

Ferberite:  The  Boulder  deposits  are  rather  remarkable  for 
the  almost  complete  absence  of  minerals  commonly  associated 
with  tungsten  ores  in  other  parts  of  the  world.  The  ore  is 
mainly  in  the  form  of  a breccia,  the  fragments  of  which  include 
chalcedonic  quartz  or  hornstone,  dike  granite  and  pegmatite, 
country  rock  and  ferberite.  The  dike  rock  shows  various  stages 
of  alteration  from  that  in  which  the  original  character  is  read- 
ily made  out  to  forms  in  which  the  original  materials  are  al- 
most entirely  replaced  by  silica.  The  matrix  is  very  commonly 
ferberite,  but  in  that  ore  in  which  fragments  of  ferberite  occur 
a matrix  of  crushed  rock  or  of  hornstone  may  partly  or  almost 
wholly  replace  the  ferberite.  Pyrite  occurs  in  very  small  amount, 
and  a rare  crystal  of  galena  is  found.  Fluorspar  has  been  re- 
ported, but  the  writer  has  not  seen  any.  There  are,  however, 
very  minute  cubical  cavities  and  a few  minute  grains  of  an 
isotropic  mineral  in  the  silicified  dike  rock  gangue  and  in  the 
hornstone.  These  cavities  may  have  been  occupied  by  fluorite, 
and  the  isotropic  grains  may  be  fluorite.  A few  very  small 
flakes  of  molybdenite  have  been  found,  and  at  one  or  two 
points  near  Magnolia  and  near  Sunshine  gold  tellurides  are  as- 
sociated with  the  ferberite. 

TUNGSTEN  LOCALITIES  IN  THE  UNITED  STATES. 

Tungsten  minerals  have  been  reported  from  about  sixty  lo- 
calities in  the  United  States.  In  the  following  list  the  numbers 
refer  to  the  accompanying  sketch.  (Plate  1.)  The  dots  mark 
places  which  have  produced  ore ; the  circles  indicate  the  presence 
of  tungsten  minerals — rarely  in  commercial  quantity. 


PLATE  I. 


50 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


)TAT1 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  51 

Washington: 

1.  Near  Loomis,  Cascade  Mts.,  Okanogan  Co.  Wolfram- 
ite. Shipping.  (68),  (76),  (93). 

2.  Vicinity  of  Deer  Trail,  Stevens  Co.  Two  localities.  (54), 
(76). 

3.  Cedar  Canyon  and  Springdale  District,  Stevens  Co. 
Opened  up.  (76). 

Oregon: 

4.  Virtue  district,  east  of  Baker  City.  Scheelite  in  placer 
gravels  of  Cliff  mine.  (87). 

California: 

5.  Eureka,  Humboldt  Co.  Tungsten  mineral  not  specified. 

(4). 

6.  Howard  Hill,  Grass  Valley,  Nevada  Co.  (86). 

7.  Twelve  miles  northeast  of  Raymond,  Madera  Co.,  and  in 
southern  Mariposa  Co.  Scheelite.  (93). 

8.  Caliente,  Amalie  and  Paris,  Kern  Co.  Scheelite  in  a 
lead-silver  mine  at  Caliente.  Producing.  (76),  (93). 

9.  Randsburg  and  Johannesburg  district  in  Kern  and  San 
Bernardino  counties.  The  Atolia  Mining  Co.  Scheelite.  Pro- 
ducing. (76),  (92),  (125r) . 

10.  Ivanpah  district.  Wolframite  occurs.  No  production 
reported.  (125k). 

11.  Sierra  Madre,  Los  Angeles  Co.  Tungsten — minerals  not 
specified.  (4) . 

12.  Near  Kelso,  on  the  Salt  Lake  Road.  Scheelite.  (93). 

13.  Manvel  and  Signal.  Scheelite.  Producing.  (125r). 

14.  Julian,  San  Diego  Co.  Tungsten — minerals  not  speci- 
fied. (4). 

Arizona: 

15.  Cochise  Co.,  six  miles  north  of  Dragoon,  on  the  A.  T. 
& S.  F.  Produced.  (91),  (97). 

16.  Whetstone  Mts.  Euclid  Mining  Co.  Operated  wol- 
framite mines  in  1906.  (76) . 

17.  Near  Arivaca,  in  Santa  Cruz  Co.  Hubnerite  has  been 
mined.  (13),  (91). 

18.  Santa  Catalina  Mts.,  near  Southern  Bell  Gold  Mine. 
Scheelite.  (13). 

19.  On  Buffalo-Arizona  Company’s  property,  near  Phoenix. 

Ore  reported.  (76). 


52 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


20.  Sixty  miles  south  of  Hackberry,  in  Aquarius  Mts.,  Mo- 
have Co.  (91),  (125p) . 

21.  Near  Owens,  80  miles  south  of  Kingman  and  12  miles 
east  of  Big  Sandy  river.  Wolframite.  Small  shipment  in  1905. 
(92). 

Nevada: 

22.  Mammoth  District:  Hubnerite.  This  is  the  place  of 
the  original  discovery  of  hubnerite.  (34) . 

23.  Lander  Co.  Ore  reported.  (77). 

24.  Near  Atwood,  Nye  Co.  Tungsten  ore.  (1251). 

25.  Tungsten  Mining  District,  12  miles  south  of  Osceola,  in 
White  Pine  Co.  Producing.  (121),  (122). 

26.  Round  Mountain.  Hubnerite.  Producing,  1907.  (13), 

(125m). 

27.  Forty  miles  south  of  Lovelocks,  Humboldt  Co.  Wol- 
framite. Considerable  development.  Shipped  1908.  (92),  (125w). 

Utah: 

28.  Little  Cottonwood.  Tungsten  ore.  No  shipment  in 

1905.  (75). 

Idaho: 

29.  Patterson  Creek,  Lemhi  Co.  Hubnerite  and  wolfram- 
ite. (125n). 

30.  Near  Murray,  Wallace  and  Mullan,  Coeur  d’Alene  dis- 
trict. Producing.  (6),  (13),  (86),  (101). 

Montana: 

31.  Near  Helena.  Scheelite. 

32.  Near  Neihart.  Scheelite.  (92). 

33.  Missoula  Co.,  western  part.  Scheelite.  Shipped  in 

1905.  (92). 

34.  Near  Phillipsburg.  Hubnerite.  (26). 

35.  Birdie  Mine,  east  of  Butte.  Hubnerite.  (125x). 

36.  Near  Jardine  and  Crevasse,  Park  Co.  Scheelite.  Pro- 
duced. (13),  (93). 

Wyoming: 

37.  Jackson  Hole  region,  near  Elk.  Wolframite.  (57). 

38.  Fremont  county,  near  Shoshone.  Tungsten  ore.  (76). 

39.  Holmes  (near).  Wolframite.  (92). 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


53 


Colorado: 

40.  Boulder  Co.,  and  adjacent  parts  of  Gilpin  Co.  (117). 

41.  Leadville.  Several  mines  report  wolframite  and 
hubnerite.  (125y). 

42.  Near  Salida.  Hubnerite  in  a vein  worked  for  copper. 
Scheelite  also  occurs  in  Chaffee  Co.  (Personal  correspondence). 
(15). 

43.  Ouray  County,  Uncompahgre  District,  Royal  Albert 
vein.  (34). 

44.  Red  Mountain  and  Gladstone,  in  San  Juan  region. 
Hubnerite.  Produced.  (95),  (96). 

New  Mexico: 

45.  Bonito.  Hubnerite  occurs.  (34). 

46.  Steins  Pass,  Lordsburg  and  Separ.  Hubnerite  and 

wolframite  shipped  in  1895-6.  (15),  (91),  (93). 

47.  Victorio  district,  18  miles  west  of  Deming.  Hubnerite 
md  scheelite.  (57). 

Texas: 

48.  Falls  County — ore  reported.  (77). 

South  Dakota: 

49.  Lawrence  Co.,  Durango,  Sula,  Harrison,  Golden,  Sum- 
mit and  Two  Strike  mines  produced  106  tons  wolframite  con- 
centrates. carrying  38-50%  tungstic  oxide.  (17). 

50.  Near  Hill  City,  Pennington  Co.  Producing.  (76). 

51.  Custer  County.  Producing.  (15). 

52.  Keystone,  Pennington  County.  Wolframite.  Produc- 
ing (?)  (76). 

Missouri: 

53.  Madison  and  St.  Francois  Co.,  in  vicinity  of  Mine  La 
Motte.  Wolframite.  (34). 

North  Carolina: 

54.  Flowe,  Cosby  and  Cullen  mines  of  Cabarrus  Co. 
Scheelite  with  a little  wolframite.  (86). 

Virginia: 

55.  Rockbridge  County.  (77). 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


54 


Connecticut: 

56.  Long  Hill  station.  {Monroe  and  Trumbull  are  included 
in  the  reference).  (59). 

Maine: 

57.  Blue  Hill  Bay.  (34). 

IMPORTANT  TUNGSTEN  DEPOSITS  IN  THE  UNITED  STATES. 

(Omitting  Boulder  County,  Colorado.) 

Arizona:  The  most  important  producing  districts  have  been 
that  near  Dragoon,  in  Cochise  county,  and  that  at  Gigas,  near 
Arivaca,  in  Santa  Cruz  county. 

In  the  Dragoon  area  hubnerite  occurs  unevenly  distributed 
in  vertical  quartz  veins,  of  irregular  width,  cutting  granitic, 
gneissoid  rocks.  The  production,  has  come  mainly  from  shal- 
low lode  workings  and  placer  washings.  In  the  Arivaca  area 
hubnerite  is  found  in  most  of  the  gold-bearing  quartz  veins  South- 
ward into  Sonora.  The  mineral  occurs  in  blade-like  crystals, 
tabular  masses  and  bunches,  and  is  easily  concentrated.  Hun- 
dreds of  tons  of  high-grade  ore  were  mined  and  piled  up  years 
ago,  and  are  still  untouched. 

California:  The  Randsburg  district,  mainly  in  San  Bernar- 
dino county,  has  become  the  second  largest  producer  of  tungsten 
ores  in  the  United  States.  Scheelite  deposits  are  found  over 
an  area  of  several  square  miles.  The  deposits  owned  and  worked 
by  the  Atolia  Mining  Company  at  Atolia,  five  miles  south  of 
Randsburg,  are  the  best  developed  in  the  district.  The  scheelite 
bearing  veins  occur  mainly  in  a medium-grained  granodiorite 
in  the  form  of  a large  mass  or  batholith  intruding  ancient  mica 
and  hornblende  schists.  On  the  north  border  of  the  mass,  veins 
occur  in  both  schist  and  granodiorite,  and  below  the  surface  may 
pass  from  one  rock  to  the  other.  The  vein  system  occupies  a 
zone  of  shearing  in  which  the  movement  was  localized  along  cer- 
tain lines.  The  vein  matter  consists  of  crushed  granodiorite, 
"partially  silidified  crushed  granodiorite,  calcite,  fine  granular 
quartz  replacing  the  granodiorite,  crystalline  quartz  and  schee- 
lite. The  quartz  and  scheelite  were  apparently  brought  up  in 
solution  and  deposited  at  the  same  time. 

Nevada:  The  Tungsten  Mining  District  lies  along  the  west- 
ern slope  of  the  Snake  Range  south  of  Wheeler  Peak,  about  45 
miles  southeast  of  Ely.  The  hubnerite  veins  are  in  a granite 
porphyry  which  intrudes  the  Cambrian  quartzites  and  argillites 
flanking  the  range.  The  veins  trend  northeast  and  southwest  and 


MAIN  TUNGSTEN  AREA  OP  BOULDER  COUNTY.  55 

pitch  55°-75°  to  the  northwest  or  southeast,  and  range  from  a 
few  inches  to  three  feet  in  width.  The  gangue  is  compact  quartz 
and  hubnerite,  with  here  and  there  a little  fluorite,  pyrite  and 
scheelite.  The  hubnerite  occurs:  (a)  irregularly  distributed 
through  the  quartz,  (b)  in  irregular  masses,  (c)  in  segregations 
along  the  vein  wall.  The  veins  were  probably  filled  by  deposi- 
tion from  mineralizing  waters  from  the  cooling  granite  porphyry. 

South  Dakota — Lead  City,  Black  Hills:  Wolframite  occurs 
in  flat,  horizontal,  but  rather  irregular  masses,  from  an  inch 
to  two  feet  thick,  and  ranging  in  area  from  20  to  30  square  feet. 
The  ore  is  intimately  associated  with  the  oxidized,  refractory, 
siliceous  gold  ores.  These  ores,  in  their  unoxidized  form,  con- 
sisted of  secondary  silica  with  pyrite,  fluorite,  barite  and  occa- 
sionally gypsum,  and  resulted  from  the  replacement  of  Cambrian 
dolomite  through  the  agency  of  uprising  (thermal)  solutions  from 
the  underlying  pre-Cambrian  schists  and  slates.  The  wolframite 
may  be  regarded  as  a basic  phase  of  the  siliceous  ores.  It  also 
occurs  as  a rim  around  the  outer  edge  of  the  siliceous  ore  shoots 
and  sometimes  as  a cap  over  them.  The  wolframite  ore  is  a 
dense,  black,  massive  rock  of  fine  texture,  resembling  a fine 
grained  magnetite. 

In  the  Nigger  Hill  and  Etta  tin  district  it  occurs  as  a con- 
stituent of  pegmatitic  granites,  usually  of  the  greisen  type. 

A number  of  other  deposits  occur  in  the  Black  Hills  region. 

Colorado — San  Juan:  Hubnerite  is  found  in  a number  of 
mines  and  prospects  near  Gladstone,  north  of  Silverton;  in  the 
Tom  Moore  lode,  one  and  one-half  miles  above  Eureka,  on  the 
Animas ; and  in  three  or  more  properties  on  the  slopes  of  Sultan 
Mountain.  It  was  found  in  the  Royal  Albert  vein  in  the  Uncom- 
pahgre  district,  Ouray  County. 

The  Adams  claim  is  on  the  western  slope  of  Bonita  Peak, 
about  a mile  from  Gladstone.  The  hubnerite  is  irregularly  dis- 
tributed as  thin  lenses,  bunches  and  stringers  in  a gangue  of 
quartz  and  fluorite  filling  a series  of  fissures  forming  a narrow 
sheeted  zone  in  an  altered  pyroxene  andesite.  In  Dry  Gulch,  a 
tributary  of  Cement  Creek,  below  Gladstone,  the  Dry  Gulch,  Dawn 
of  Day,  Sunshine  and  Minnesota  claims  are  located  on  a single 
strong  lode.  Hubnerite  occurs  in  all  the  claims,  but  only  the 
Dry  Gulch  and  Dawn  of  Day  show  any  important  development. 
The  occurrence  of  the  hubnerite  is  similar  to  that  in  the  Adams. 
A few  tons  of  high-grade  concentrates  have  been  shipped.  The 
Natalie  and  Big  Colorado  mines  are  in  a gulch  a short  distance 


56  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

southeast  of  Gladstone.  The  Natalie  hubnerite  is  in  glistening, 
black  needles,  prisms  and  blades  in  a quartz  gangue.  Amorphous 
silica  sometimes  forms  smooth  rounded  surfaces  over  the  quartz 
and  hubnerite.  The  ore  resembles  wolframite,  but  the  analysis 
(page  44)  shows  only  2.03  per  cent.  FeO.  It  pulverizes  to  a 
rich  brown  powder.  The  other  metallic  minerals  of  the  Natalie 
include  argentiferous  galena,  pyrite,  chalcopyrite  and  free  gold. 

The  hubnerite  of  the  Tom  Moore  is  in  very  small  quantity 
and  can  not  be  regarded  as  at  all  promising.  The  North  Star 
mine,  the  Little  Dora  vein  and  the  Empire-Victoria  vein  are  all 
on  the  slopes  of  Sultan  mountain.  All  contain  a little  hubnerite. 
The  ores  include  auriferous  pyrite,  galena,  tetrahedrite,  chalco- 
pyrite, sphalerite,  associated  with  fluorite,  barite  and  much 
quartz.  Hubnerite  occurs  associated  with  fluorite  in  the  more 
quartzose  portion  of  the  veins,  though  occasionally  it  is  in  a kaol- 
inized,  disintegrated  mass.  Both  fluorite  and  hubnerite  are  later 
than  the  main  vein  filling.  The  country  rock  is  monzonite. 

The  conditions  would  seem  to  be  favorable  for  making  tung- 
sten concentrates  as  a valuable  by-product,  but  the  showings,  as 
yet,  do  not  promise  profits  if  tungsten  alone  is  produced. 

FOREIGN  OCCURRENCES. 

Australasia:  Tungsten  ores  are  mined  in  Queensland,  New 
South  Wales  and  the  Northern  Territory  (of  South  Australia), 
and  they  are  reported  from  various  points  in  West  Australia. 
In  production  the  states  stand  in  the  order  named. 

In  northern  Queensland  an  area  of  3,500  square  miles  con- 
tains several  belts  of  tungsten  deposits.  The  ore  is  almost  ex- 
clusively wolframite,  though  scheelite  is  produced  in  one  lo- 
cality (Parada).  Both  lode  and  placer  mining  are  carried  on. 
Old  Wolfram  Camp  is  the  most  important  tungsten  mining 
centre.  The  commonest  country  rock  of  the  tungsten  area  is 
granite,  but  deposits  are  also  found  in  greisen,  felsite,  quartz- 
porphyry,  chlorite  schist,  slate,  and  quartzite.  “The  gangue  of 
the  wolframite  is  usually  quartz,  but  it  also  occurs  with  and 
without  this  mineral  in  greisen,  chlorite,  muscovite,  biotite, 
topaz  rock,  fluorspar,  and  beryl-rock.”  In  form,  the  ore  bodies 
include  quartz  veins,  large  and  lenticular  bodies  of  quartz,  ir- 
regular masses  of  chlorite,  quartz  and  mica,  and  impregnations 
of  greisen  and  granite.  In  the  richest  ore  bodies,  those  of  ir- 
regular form,  the  wolframite  occurs  in  isolated  patches  or 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  57 

bunches.  Bismuth  and  molybdenum  are  saved  as  by-products. 
Tin  is  also  important. 

South  Australia:  Tungsten  ores  are  found  in  the  Northern 
Territory,  and  have  been  extensively  mined  during  the  past  two 
years. 

West  Australia:  Tungsten  ore  occurs  in  the  Geraldton, 
Pilbarra,  Coolgardie  and  Greenbush  areas. 

New  South  Wales:  Scheelite  is  mined  at  Hill  Grove,  and 
wolframite  in  the  Mole  Table  land.  Producing  areas  are:  Em- 
maville,  Uralla  Tuena,  Baraba,  and  Farrington. 

New  Zealand,  Otago:  Scheelite  occurs  in  the  auriferous 
quartz  reefs  of  Otago  and  Marlborough.  The  reef  follows  the 
planes  of  schistosity  of  the  schists. 

Tasmania:  A few  tons  of  wolframite  are  produced. 
Europe: 

Portugal  produces  a few  hundred  tons  of  ores  annually, 
chiefly  from  the  province  of  Beira  Baixa,  where  wolframite  oc- 
curs with  tin  ore,  oxide  of  iron,  pyrite,  arsenopyrite  and  mica 
in  quartz  gangue  in  schists  of  Cambrian  age.  Portugal  has  be- 
come the  largest  European  producer. 

England:  Wolframite,  scheelite  and  tungsten  ochre  occur 
both  in  the  mines  and  in  the  tin  placers  of  Cornwall,  chiefly  in 
the  high-level  platforms  of  Bodmin  Moor.  But  wolframite  is 
the  only  commercially  important  ore.  It  accompanies  tin 
and  copper  ores  which  occur  disseminated  through  granites, 
quartz  porphyry  (“elvan”)  and  slates  (“killas”),  and  in 
minute  veins  in  these  rocks.  As  Camborne  is  the  most 
important  area,  a brief  description  will  be  given.  Meta- 
morphic  sediments  varying  in  character  from  slates  to  phyl- 
lites  overlying  granites  are  intruded  by  greenstone  sheets,  and 
both  slate  and  greenstone  are  cut  by  large  granite  masses  hav- 
ing an  average  trend  of  20°  north  of  east.  Cutting  all  these  are 
dikes  of  quartz  porphyry.  The  area  is  cut  by  many  faults  trend- 
ing almost  at  right  angles  to  the  quartz  porphyry  dikes  and 
the  mineral  lodes. 

The  lodes  are  commonly  parallel  to  the  dikes  and  in  many  in- 
stances occupy  fault  planes.  The  walls  are  irregular  and  im- 
pregnation of  the  country  rock  is  common.  The  ore  is  irregu- 
larly distributed  in  the  lodes  in  “bunches  and  pipe-like”  masses, 
and  there  are  many  evidences  of  secondary  enrichment.  The 
mineral  contents  include,  (1)  the  “veinstone,”  which  may  be 
quartz,  feldspar  and  tourmaline  and  decomposition  products 


58 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


from  the  country  rock;  (2)  the  ores  or  metalliferous  minerals, 
including  cassiterite,  pyrite,  arsenopyrite,  chalcopyrite,  and  wol- 
framite. Locally,  ores  of  nickel,  cobalt,  zinc,  lead  and  uranium 
are  found  in  the  higher  levels,  while  antimony,  bismuth  and 
molybdenum  have  been  produced  in  commercial  quantity.  The 
tungsten  ore  is  mainly  wolframite,  but  scheelite  and  tungsten 
ochre  occur.  The  wolframite  occurs  along,  and  on  both  sides 
of  the  contact  between  the  granite  and  the  slate.  The  Cam- 
borne district  is  the  most  important  tungsten  producer,  but 
shipments  have  been  made  from  Tavistock,  especially  from  the 
Clitters  mine,  and  from  near  Liskeard. 

Spain:  Wolframite  and  scheelite  occur  in  La  Sorpresa 
mine,  in  a white  quartz  at  the  contact  of  Cambrian  slates  and 
granite.  The  tin  deposits  of  Orense  and  Pontevedra  carry  wol- 
framite. 

Austria:  Produces  a small  tonnage  annually,  mainly  as  a 
by-product  of  the  tin  mining. 

Germany:  A few  tons  of  tungsten  concentrates  are  pro- 
duced annually  from  the  old  tin  dumps  of  the  Altenburg  dis- 
trict. 

Italy  must  be  credited  with  a few  tons. 

France  produces  a few  tons. 

Sardinia : Scheelite  and  wolframite  have  been  found  in 
considerable  quantity. 

Russia:  Tungsten  ore  has  been  mined  in  the  Ural  Moun- 
tains. 

Africa: 

South  Africa  became  a tungsten  producer  in  1906,  and  in 
1907  shipped  211  tons,  on  a 60  per  cent,  tungstic  oxide  basis. 

Asia: 

India:  Wolframite  is  found  in  the  Tenasserim  district  of 
Burma,  and  at  Agargaon. 

Siam,  the  Federated  Malay  States,  Singkep  and  Billiton,  all 
produce  a small  tonnage  of  tungsten  ore.  Most  of  this  is  ob- 
tained as  a by-product  of  tin  mining. 

Siberia:  Hubnerite  and  wolframite  are  reported  from  the 
gold  mines. 

South  America: 

Argentina  has  outstripped  all  other  South  American  states. 

Bolivia : Wolframite  is  mined  chiefly  in  the  tin-mining  dis- 
tricts of  La  Paz,  Oruru,  Potosi,  and  Chorolque. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  59 

Brazil:  Promising  deposits  have  been  opened  near  Porte 
Alegre,  South  Brazil. 

Canada: 

Nova  Scotia:  Wolframite  occurs  at  Northeast  Margaree, 
and  hubnerite  at  Emerald,  in  Inverness  county.  Scheelite  is 
found  in  the  Molega  mining  district,  Queens  county.  Wolfram- 
ite, hubnerite,  and  scheelite  are  found  in  the  tin  deposits  at 
New  Ross,  Lunenburg  county. 

Quebec:  Scheelite,  sometimes  accompanied  by  tungstite 
(or  meymacite),  occurs  in  Marlow  township,  Beauce  county. 

Ontario:  Wolframite  was  found  in  a boulder  on  Chiefs 
Island,  Simcoe  county,  and  scheelite  has  been  found  at  Sudbury. 

British  Columbia:  Scheelite  occurs  in  the  Slocan  district 
and  near  Barkerville  in  the  Cariboo  district.  Wolframite  and 
scheelite  occur  on  Sheep  Creek,  near  Salmo,  in  the  Kootenay 
and  wolframite  occurs  on  St.  Mary's  River  north  of  Cranbrook. 

Yukon:  Scheelite  has  been  found  in  the  placers. 

The  world's  production  of  tungsten  ore  for  1906  and  1907: 
The  table  is  arranged  according  to  production  for  1907,  esti- 
mated in  short  tons  of  concentrates  containing  60  per  cent,  of 
tungstic  oxide:  (From  Mineral  Resources  for  1907.) 


Country.  1907  1906 

United  States  1,640  928 

Queensland  703  865 

Portugal  702  629 

Argentine  507  326 

New  South  Wales 451  270 

Northern  Territory  (Australia) 443  114 

England  361  304 

Spain  222  222 

South  Africa 211  9 

New  Zealand 121  121 

Federated  Malay  States - 89  151 

Bolivia 75  75 

Austria  63  63 

German  Empire  57  57 

Tasmania 46  22 

Billiton  41 

Italy  28  28 

France  20  20 

Siam 1°  

Singkep 1 


Total * 5,791  4,204 


60 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


ORE-BODIES  OF  BOULDER  COUNTY. 

Country  rock:  The  granite,  gneissoid  granite,  and  the  more 
granitic  parts  of  the  gneiss  have  proved  the  best  ground  for  the 
prospector  and  miner.  The  majority  of  the  mines  are  in  the 
granite  area  of  the  map,  but  a number  of  the  good  producers  lie 
close  to  the  contact  of  granite  and  gneiss,  and  in  some  instances 
the  workings  are  almost  entirely  within  the  gneiss.  It  is  a no- 
ticeable fact,  however,  that,  where  the  veins  cut  the  more  pro- 
nounced gneiss,  and  particularly  the  schistose  bands  and  areas 
of  the  gneiss  the  ore-bodies  decrease  in  size  and  not  infrequently 
the  vein  becomes  barren.  This  is  due  to  the  physical  rather  than 
to  the  chemical  character  of  the  rock.  In  the  deformations  and 
faultings  which  prepared  the  openings  for  the  ore  deposits,  the 
gneissoid  granite,  the  less  schistose  parts  of  the  gneiss  and  the 
pegmatite  were  intimately  fractured  and  formed  rather  open 
breccias.  On  the  other  hand,  the  schistose  part  of  the  gneiss, 
acting  more  as  a plastic  mass,  yielded  by  folding,  crumpling  and 
shearing,  rather  than  by  open  fracturing,  and,  adjusting  itself 
to  the  entire  space  available,  closed  up  the  underground  water 
courses.  In  the  Nederland-Beaver  Creek  area  a number  of  the 
veins  follow  dikes  of  coarse  and  fine  pegmatite,  but  the  relation- 
ship is  due  to  structure  rather  than  to  any  common  genesis.  The 
fissuring  now  occupied  by  the  veins — long  subsequent  to  the  for- 
mation of  the  pegmatite  dikes — followed  the  lines  of  least  resist- 
ance, which,  in  several  instances,  coincided  with  the  dikes.  In  the 
northeastern  area  pegmatite  is  not  so  abundant  and  there  are  few 
associations  of  ore  and  typical  pegmatite. 

Other  veins  are  associated  with  a fine  grained  intrusive  bio- 
tite  granite  which  forms  dikes  and  irregular  masses  such  as  that 
about  the  Clyde  Mine,  a mile  northeast  of  Nederland.  In  some 
instances,  particularly  in  the  southeastern  area,  this  fine-grained 
granite  shows  a tendency  toward  the  porphyritic  texture,  but  this 
seems  to  be  merely  a local  variation  which  is  not  characteristic. 
Weathering  has  made  the  porphyritic  appearance  more  prominent 
in  many  places,  while  in  other  instances  it  has  given  the  rock 
somewhat  the  appearance  of  a decayed  greisen.  The  biotite  has 
become  leached  and  chloritized,  and  a chloritized  kaolin  occurs 
in  grains  of  considerable  size.  In  some  cases  the  fine-grained 
granite  seems  to  grade  imperceptibly  into  the  country  granite. 
This  may  be  due  in  part  to  contact  metamorphism,  for  it  is  evident 
that  in  places,  mineral  changes  have  taken  place  along  the  line 
of  contact,  which  have  rendered  the  two  rocks  more  alike. 


PLATE  II. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY, 


61 


62  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

The  relationship  of  the  veins  to  the  dikes  is  the  same  in  the 
line-grained  granite  as  in  the  pegmatite.  The  fractures  occupied 
by  the  veins  commonly  follow  one  or  other  wall  of  the  dike.  Oc- 
casionally they  split  the  dike  and  both  walls  of  the  vein  are 
formed  by  the  dike  rock.  In  some  cases  the  vein  leaves  the  dike 
entirely  and  passes  out  into  the  country  rock,  usually  at  a sharp 
angle  with  the  dike,  leaving  a thin  wedge  of  country  rock  be- 
tween. In  the  northeastern  area  the  long  line  of  mines  and  pros- 
pects roughly  parallel  to  Middle  Boulder  and  Boulder  Creeks 
from  near  Castle  Rock  to  Wheelmen  is  closely  associated,  in  a 
large  part  of  its  course,  with  a narrow,  but  rather  continuous 
dike  of  fine-grained  granite.  In  places  the  entire  width  of  the 
dike  is  occupied  by  the  vein.  In  others,  alteration  in  both  the 
dike  and  the  country  rock  has  left  the  two  quite  similar  in  ap- 
pearance. 

Trend  of  the  veins:  There  is  no  regular  system  of  veins  such 
as  characterizes  certain  camps.  But  in  the  Nederland  and  Beaver 
Creek  part  of  the  field,  a large  proportion  of  the  veins  trend  be- 
tween north  and  east,  ranging  from  due  north  to  north  80°  east. 
Very  few  take  a course  west  of  north.  The  average  trend  of  eleven 
well-defined  veins  in  the  western  part  of  the  Nederland-Beaver 
Creek  area  is  north  32°  east,  but  the  courses  nearest  to  the  aver- 
age are:  N.  24°  E.,  N.  29°  E.,  N.  40°  E.,  N.  40°  E.  In  the  Upper 
Rogers  Tract  eight  veins  average  N.  45°  E.,  and  one  other  has  a 
trend  N.  87°  E.  Fifteen  veins  of  the  Lower  Rogers  Tract  range 
from  N.  48°  E.,  to  N.  70°  E. 

In  the  Gordon  Gulch  area  the  general  trend  is  north  of  east, 
but  is  much  more  nearly  east  and  west  than  in  the  Nederland- 
Beaver  Creek  area. 

The  angle  of  dip  of  the  veins  is  generally  steep — often  ap- 
proaching the  vertical,  and  rarely  falling  so  low  as  45°.  The 
following  are  a few  examples  of  the  trend  and  dip  of  the  veins: 
The  Townlot — trends  north  and  south,  and  dips  65°  E.,  but  flat- 
tens to  40°  ©r  45°.  The  Conger  trends  N.  8°  E.,  and  dips  at  a 
variable,  but  always  high  degree,  west.  The  Oregon  trends  N. 
8C  E.,  and  dips  at  a high  degree  west.  The  Beddick  trends  N.  20" 
E.  (general).  The  Elsie  trends  N.  62°  E.  and  dips  nearly  90°. 
The  Last  Chance  trends  N.  40°  E. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


63 


VEIN  STRUCTURE  AND  VEIN  FILLING. 

Outline  of  the  stages  of  ore-deposition  in  the  Nederland- 
Beaver  Creek  part  of  the  field: 

a.  The  first  opening  of  the  fissures,  accompanied  by  much 
crushing  and  the  formation  of  masses  of  angular  fragments. 

b.  The  silicification  of  the  rock  fragments  and  their  par- 
tial cementation  into  an  open  breccia,  and  a slight  local  deposi- 
tion of  tungsten  mineral. 

c.  The  second  movement  of  brecciation. 

d.  The  first  important  deposition  of  tungsten  mineral. 

e.  The  third  movement,  crushing  the  breccia-ore,  and  min- 
gling it  with  much  rock  matter,  and  in  places  forming  a new 
breccia  by  pressure. 

f.  The  second  deposition  of  chalcedony-like  silica.  This  was 
local. 

g.  The  second  important  tungsten  deposition,  partially  ce- 
menting the  breccia.  It  is  possible  that  this  was  a secondary 
enrichment.  But  no  clear  evidence  was  found. 

h.  The  contemporaneous  deposition  of  silica  and  tungsten. 

i.  Local  solution  of  the  tungsten  and  deposition  of  silica. 

(j.  In  parts  of  the  tungsten  field  slickensiding  and  very  re- 
cent brecciation  are  found,  showing  that  movement  has  occurred 
later  than  recognizable  deposition  of  ferberite  or  silica.) 

While  the  stages  outlined  above  are  not  all  evident  in  all 
the  tungsten  deposits,  they  are  clearly  recorded  in  several  of 
those  affording  the  best  opportunity  for  investigation,  and  it 
seems  probable  that  further  study  would  show  that  for  the  Ne- 
derland-Beaver  Creek  part  of  the  field  the  stages  in  the  forma- 
tion of  the  deposits  were,  in  general,  as  here  indicated.  Owing 
to  the  closing  of  most  of  the  mines  before  the  field  work  of  the 
northeastern  area  was  completed,  the  ore  bodies  could  not  be 
studied  in  detail,  but  it  is  probable  that  the  process  of  deposi- 
tion was  less  complex  and  accompanied  by  fewer  movements. 

a Many  of  the  first  fissures  followed  pegmatite  and  biotite 
granite  dikes  while  others  cut  the  country  rock.  They  were  the 
result  of  tensional  stresses,  accompanied  or  followed  by,  both 
horizontal  and  vertical  movements  in  which  the  dislocation  was 
probably  slight.  When  the  movements  ceased,  the  fissures  were 
partially  filled  by  loose,  open  masses  of  angular  rock  fragments, 
varying  in  size  from  mere  grains  to  boulders.  In  the  pegmatite 
dikes  the  crushing  resulted  in  the  formation  of  smaller  frag- 


64  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

ments  than  in  the  biotite  granite  dikes.  The  large  feldspars 
split  easily  along  cleavage  planes,  and  many  of  the  fragments 
contain  only  feldspar,  while  others  show  only  quartz.  But  the 
zone  of  fracturing  was,  as  a rule,  narrower  in  the  pegmatite  than 
in  the  dike  granite,  or  in  the  country  rock. 

Where  the  fissures  have  followed  dikes,  the  position  of  the 
fissure  with  respect  to  the  dike  walls  seems  to  have  influenced 
the  location  of  the  crushing.  Where  the  fissure  is  within  the 
dike,  the  crushing  is  generally  on  both  sides  of  the  opening,  but 
where  the  fissure  follows  one  of  the  dike  walls,  the  dike  rock  is 
usually  much  more  crushed  than  is  the  country  rock.  This  may 
be  due  in  part  to  the  yielding  of  the  country  rock  without  marked 
fracturing  along  the  more  or  less  distinct  foliation  planes,  or  it 
may  be  due  to  the  greater  strength  of  the  country  rock. 

b Silica-bearing  waters,  probably  at  high  temperature,  cir- 
culated through  the  rock  fragments  in  the  fissures.  By  a process 
of  replacement  the  feldspars  and  the  biotite  of  the  rock  fragments 
were  slowly  dissolved  out,  and  silica  in  the  form  chalcedony-like 
quartz  or  hornstone  was  deposited  in  their  place.  By  this  sub- 
stitution many  of  the  smaller  rock  fragments  were  almost  en- 
tirely robbed  of  their  feldspar  and  biotite,  and  are  not  easily  dis- 
tinguished from  the  hornstone.  In  others,  an  occasional  feldspar 
and  a few  semi-transparent  quartz  grains  remained  to  show  the 
original  character  of  the  rock.  The  larger  fragments  still  re- 
tained cores  of  unaltered  rock  surrounded  by  shells,  from  which 
these  minerals  were  more  or  less  completely  removed.  That  the 
rock  fragments  were  fresh  when  the  process  of  change  began  is 
probable  from  the  facts : that  the  replacement  probably  took  place 
below  the  zone  of  weathering ; and  that  fresh  feldspars  and  biotite 
are  still  found  in  the  cores  of  the  large  fragments.  These  silica- 
bearing waters  also  deposited  hornstone  between  the  rock  frag- 
ments and  partially  cemented  them  into  an  open  breccia.  The  com- 
pletely silicified  rock-fragments  and  the  silica  cement  between 
the  fragments  are  a part  of  the  hornstone  (“hornblende”  of  the 
miners).  It  is  probable  that  a part  of  the  pegmatization  men- 
tioned in  the  discussion  of  pegmatites  took  place  at  this  time, 
and  that  the  secondary  feldspars  observable  in  some  parts  of 
the  area  represent  the  crystallization  of  the  feldspars  removed 
from  the  rock  fragments.  Locally,  a small  deposition  of  fer- 
berite  accompanied  the  silification. 

c The  breccia  in  the  fissures  was  still  very  open  when  the 
second  movement  occurred.  This  time  the  vein  breccia  with  the 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


65 


local  deposits  of  tungsten,  more  dike  rock,  and  in  places  country 
rock,  were  crushed  and  mingled  in  a new  mass  of  fragments,  ready 
to  be  cemented  into  a new  breccia.  This  movement  was  accompan- 
ied by  considerable  vertical  displacement  and  dragging  along  the 
walls  of  the  veins. 

d The  first  important  deposition  of  tungsten  followed  the 
second  crushing  movement,  which  seems  to  have  been  more  pro- 
found than  the  preceding.  The  character  of  the  waters  which 
followed  it  was  quite  different  from  that  of  those  which  followed 
the  first.  In  place  of  an  overload  of  silica,  these  were  heavily 
charged  with  tungsten  salt,  and  either  through  changed  physical 
conditions  as  they  rose  to  the  surface  or  through  mingling  with 
other  solutions — probably  carrying  ferrous  iron,  ferberite  was 
deposited.  In  places  silica  accompanied  the  deposition  of  fer- 
berite in  the  earlier  part  of  the  process.  This  may  have  been  the 
overlapping  of  the  two  processes  of  deposition,  since  the  earliest 
tungsten  precipitation  began  before  the  second  movement  as  men- 
tioned above. 

In  less  open  parts  of  the  fragmental  mass  in  the  fissures  the 
ferberite  formed  a complete  cementation,  but  in  the  more  open 
parts  the  walls  of  the  openings  were  crustified  and  many  vug- 
like cavities  were  formed  by  the  connecting  crusts  of  ferberite. 
Locally,  silica  deposition  followed  the  ferberite  before  the  third 
movement  took  place,  but  this  was  not  general. 

e The  third  movement  crushed  the  vein  filling  and  added 
dike-rock  or  country-rock  to  the  fragmental  mass.  It  now  consist- 
ed of  the  silicified  dike-rock  or  country-rock  in  varying  amount, 
chalcedonic  quartz  and  the  ferberite.  Locally  this  movement 
caused  the  formation  of  a pressure-cemented  breccia.  Probably 
silica  aided  the  cementation. 

f The  second  considerable  deposition  of  hornstone  silica 
followed  the  third  movement  and  partially  recemented  the  frag- 
ments, but  this  was  only  local. 

g The  second  important  tungsten  deposition  followed  the 
third  movement,  and  in  places  completed  the  cementation,  but 
much  open  ground  still  remains  in  the  veins,  and  vugs  lined  with 
ferberite  druses  are  very  common.  It  is  possible  that  this  was  a 
secondary  enrichment  in  which  the  tungsten  of  the  higher  parts 
of  the  vein  was  dissolved  and  carried  down  and  deposited  at 
greater  depth.  But  no  clear  evidence  was  found  in  support  of 
this.  The  presence  of  rich  ore  at  the  surface,  and  much  float 
in  the  mantel  rock  are  opposed  to  this  view. 


66 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


h The  contemporaneous  deposition  of  silica  and  tungsten. 
i Local  solution  of  the  tungsten  and  deposition  of  silica, 
possibly  producing  secondary  enrichment  is  quite  noticeable. 

PLATE  III. 


Pig.  3 — Conger.  Pig. 


i — Townlot.  A breccia  showing  fragments  of  ferberlte. 
See  fu'ler  description  of  plates. 


Tig.  l — Elsie  Mine.  Pig.  2 — Mammoth  Mine,  Beaver  Creek.  Breccia  ore,  com- 
sisting  of  fragments  of  dike  rock  and  country  rock  cemented  by  ferberite. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  67 

The  ores:  The  ferberite  occurs  in  three  rather  well-defined 
forms,  which,  however,  frequently  grade  into  one  another.  These 
are:  1.  Well  crystallized  crusts  and  layers  covering  the  sur- 
face of  rock  and  hornstone  fragments  and  cementing  them  into 
a rather  open  breccia ; 2.  Massive  granular  ore  showing  few  or 
no  crystal  faces  and  occurring  as  more  dense  seams  and  masses 
in  the  wider  and  less  brecciated  parts  of  the  vein ; 3.  The  highly 
siliceous  ore  in  which  ferberite  in  fine  grains — sometimes  show- 
ing crystal  forms — is  scattered  through  hornstone  or  cryptocrys- 
talline quartz.  This  type  may  occur  in  any  of  the  mines,  but 
was  probably  most  abundant  in  the  earlier  workings  of  the  east- 
ern side  of  the  region.  It  varies  widely  in  its  ferberite  content 
from  masses  in  which  hornstone  is  but  a scanty  cementing  matrix 
to  those  in  which  there  is  but  a meager  sprinkling  of  minute  fer- 
berite grains  in  the  hornstone. 

DESCRIPTION  OF  PLATES. 

Plate  III,  Figs.  1 and  2. — A very  common  type  of  ore — that 
formed  by  the  cementation  of  rock  fragments  by  ferberite.  In 
these  specimens  there  are  fragments  of  both  the  dike  rock  along 
which  the  vein  is  formed,  and  the  country  rock  cut  by  the  dike. 
This  is  common  when  the  vein  follows  one  wall  of  the  dike.  The 
dike  rock  is  a quartz-rich  granite  in  which  the  original  minerals 
are  still  visible  in  spite  of  a considerable  development  of  second 
ary  quartz  and  the  alteration  of  a part  of  the  biotite  to  muscovite. 
Some  of  the  fragments  have  lost  much  of  the  mica  and  feldspar 
from  their  outer  borders.  The  country  rock  is  a fine  grained 
gneissoid,  or  almost  schistose  rock,  showing  many  small  flakes  of 
biotite.  In  some  of  the  fragments,  ferberite  fills  cavities  formed 
by  the  solution  of  some  of  the  rock-making  minerals.  The  ce- 
mentation by  the  tungsten  ore  was  incomplete  and  vugs  lined 
with  ferberite  are  shown.  The  specimens  are  from  the  Elsie  and 
Mammoth  mines  on  Beaver  Creek. 

Figs.  3 and  4. — These  specimens  are  breccia-ore  of  different 
character  from  that  shown  in  Plate  III.  It  is  the  result 
of  one  of  the  later  movements — the  third — and  contains  the 
products  of  earlier  movements  and  earlier  depositions.  There 
are  fragments  of  country  rock,  of  hornstone,  of  pegmatite,  and  of 
ferberite.  It  is  almost  an  auto-breccia — a breccia  in  which 
there  is  no  distinct  matrix — but  a later  deposition  of  ferberite 
has  filled  a few  openings  left  by  the  crushing  and  squeezing. 
The  country  rock  was  much  altered  before  the  movement,  and 
had  lost  a large  part  of  its  feldspar,  while  that  which  remained 


68 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


was  kaolinized  and  now  forms  a dense,  very  fine-grained  matrix 
for  the  quartz  grains.  This  type  of  ore  is  common  in  the  Neder- 
land-Beaver  Creek  part  of  the  area. 

PLATE  IV. 


Fig\  5 — Townlot  Mine.  Same  g'eneral  features  as  Tig's.  3 and  4,  Plate  II,  tout 
the  breccia  is  more  open. 


Fig1.  6 — Drusy  ore  from  Elsie  Mine. 

Fig-.  7 — Drusy  ore  from  the  Graytoack. 

Plate  IV,  Fig.  5. — This  specimen  from  the  Townlot  mine 
shows  the  same  general  features  as  are  brought  out  by  Plate  II, 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  69 

Figs.  3 and  4,  but  the  breccia,  while  finer,  is  more  open  and  con- 
tains more  seams  of  ferberite  deposited  after  the  brecciation. 

PLATE  V. 


Figr.  8 — Home  Run.  Figs.  9,  10 — Boulder  Falls.  Fig-.  11 — Rogers  Tract. 
See  description  of  plates. 


Fig-.  11  A — Crystallized  ferberite- 

Plate  IV,  Figs.  6 and  7. — These  specimens  from  the  Elsie  and 
the  Grayback  show  the  drusy  linings  of  cavities.  The  rock-frag- 


70 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


PLATE  VI. 


Pig1.  12 — Shows  contemporaneous  deposition  of  quartz  and  ferfcerite. 


Pigs.  13  and  15— Clyde  Mine.  Pig*.  14 — Beddick  Mine,  See  description. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY 


PLATE  VII. 


Pig*.  18 — Conger,  reduced  one-half. 


72 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


ments  in  6 include  both  country  rock  and  pegmatite,  while  those 
in  7 show  highly  silicified  country  rock  and  hornstone. 

Plate  V,  Figs.  8,  9,  10  and  11. — Figure  8 shows  a piece  of 
ore  from  the  Home  Run  mine  of  the  Crucible  Steel  Company. 
The  rock-fragments  are  fragments  of  the  country  rock,  and  many 
of  them  are  so  completely  silicified  as  to  be  almost  indistinguish- 
able from  the  hornstone.  Figures  9 and  10  show  ore  from 
Boulder  Falls,  and  Figure  11,  ore  from  the  Rogers  Tract.  These 
ores  present  a breccia  of  dike  rock,  country  rock  and  hornstone, 
with  a ferberite  cement.  The  ore  shown  in  Figure  9 is  from 
Boulder  Falls,  and  consists  of  a breccia  of  dike  rock  fragments, 
many  of  which  are  so  highly  silicified  as  to  be  almost  indistin- 
guishable from  the  hornstone.  In  Figures  10  and  11  the  dike  rock 
fragments  are  but  slightly  silicified,  though  biotite  is  almost  ab- 
sent. 

Fig.  11  (lower)  shows  crystallized  ferberite. 

Plate  VI,  Fig.  12. — Very  open  ore,  showing  dike  fragments 
varying  from  slight  to  complete  silicification.  The  ferberite  ce- 
ment is  also  highly  siliceous  and  films  of  quartz  cover  the  drusy 
ferberite  in  some  of  the  openings.  Slickensiding  shows  move- 
ment since  the  deposition  of  the  ore. 

Fig.  13. — A breccia  of  hornstone,  highly  silicified  dike  rock 
and  ferberite,  with  a small  amount  of  cementing  silica.  The  brec- 
ciation  followed  the  deposition  of  ferberite. 

Fig.  14. — A stringer  of  breccia  ore  in  pegmatite.  The  rock- 
fragments  are  highly  silicified  pegmatite,  coated  with  drusy  fer- 
berite. Hornstone  has  completed  the  cementation. 

Fig.  15. — A stringer  of  ferberite  between  a wall  of  altered 
pegmatite  and  a wall  of  hornstone.  The  dividing  line  between 
the  ferberite  and  the  hornstone  is  just  above  the  number. 

Plate  VII,  Fig.  16. — A breccia  of  hornstone  and  dike  rock  in 
varying  stages  of  silicification.  The  last  event  was  the  deposition 
of  drusy  quartz  and  secondary  feldspar. 

Fig.  17. — A breccia  of  kaolinized  and  talcose  dike  rock  with 
a ferberite  cement. 

Fig.  18. — A stringer  of  breccia  composed  of  hornstone,  peg- 
matite and  ferberite,  reduced  one-half.  The  last  event  was  fer- 
berite deposition  along  the  fissure  walls.  A previous  movement 
brecciated  an  earlier  deposition  of  ferberite. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


73 


PLATE  VIII. 


Fig-.  19 — Colorado  Tungsten  Corporation  No.  4. 
Fig.  20 — Grayback  Mine. 


Fig.  21 — High-grade  ore  from  various  mines. 


Plate  VIII,  Fig.  19. — Dike  rock — much  decayed — cemented  by 
crystalline-granular  ferberite. 


74 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Fig.  20. — Breccia  of  altered  country  rock  cemented  by  gran- 
ular ferberite. 

Fig.  21. — High-grade  ore  from  various  mines. 

Plate  IX,  Fig.  22. — Crystallized  ferberite  from  Lone  Tree 
mine. 

PLATE  IX. 


Fig.  22 — Crystallized  ferberite,  Lone  Tree  Mine. 


Fig.  23 — Conger  and  Beddick  shaft  houses. 


Fig,  23. — Conger  and  Beddick  shaft  houses. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


75 


Gangue:  In  the  ores  of  the  first  two  types  the  gangue  ma- 
terials depend  largely  upon  the  character  of  the  rock  in  which 
the  vein  is  formed.  If  the  vein  is  in  pegmatite  the  gangue  may 
include  fragments  of  the  pegmatite,  together  with  more  or  less 
deposited  hornstone,  a pait  or  all  of  which  may  be  in  angular 
fragments.  In  the  granite  dikes  and  masses,  fragments  of  gran- 
ite will  take  the  place  of  the  pegmatite,  while  in  the  veins  cut- 
ting the  granite  and  gneissoid  granite  these  rocks  furnish  their 
share  of  the  gangue.  In  the  shallower  workings  much  of  the  rock 
matter  is  highly  altered.  In  places  this  alteration  has  gone  only  to 
the  extent  of  the  kaolinization  of  the  feldspars  and  the  removal  of 
the  dark  minerals  or  their  alteration  to  a pale  green  talcose  chlor- 
ite. Such  ores  are  the  most  easily  concentrated.  In  other  cases  the 
alteration  has  included  the  replacement  of  the  greater  part  of  the 
feldspar  by  cryptocrystalline  quartz  or  hornstone  almost  indis- 
tinguishable from  the  hornstone  deposited  from  solution.  Below 
the  surface  weathering,  the  rock  fragments  are  fresher,  silicified 
fragments  are  also  numerous,  and  hornstone  may  be  objectionably 
plentiful.  These  last  conditions  increase  the  difficulties  of  concen- 
tration and  make  a high  percentage  saving  very  hard  to  secure. 

Other  vein  minerals:  The  Boulder  veins  are  unusually  free 
from  the  minerals  which  commonly  accompany  tungsten  ores. 
Scheelite  is  occasionally  met  with  in  the  form  of  beautiful  druses 
of  dull  honey-yellow  crystals  having  perfect  pyramidal  termina- 
tions. Pyrite  occurs  in  very  small  amount  in  the  gangue,  but 
rarely,  if  ever  in  the  ferberite.  The  amount  is  so  small  that  many 
analyses  do  not  show  even  a trace  of  sulphur.  Galena  is  a very 
rare  mineral  in  the  tungsten  veins,  and  when  found  is  generally 
in  minute  cubical  grains  except  in  one  of  the  tunnels  near  Mag- 
nolia where  an  appreciable  quantity  occurs.  Sphalerite  is  as- 
sociated with  the  galena  near  Magnolia,  and  is  reported  in  minute 
quantity  from  one  or  two  other  localities.  Molybdenite  in  mi- 
nute flakes  is  found  very  sparingly  in  the  gneissoid  granite,  but 
is  exceedingly  rare.  A specimen  of  ore  from  the  Clyde  mine  shows 
a small  flake  or  two.  Magnetite  forms  small,  irregular  grains 
and  imperfect  crystals  in  both  the  pegmatite  and  the  granite 
dikes,  but  the  amount  is  very  small.  Most  of  the  ore  shows  a 
very  little  magnetite,  but  it  is  almost  impossible,  even  with  a 
very  weak  magnet,  to  get  a sample  which  will  not  react  for 
tungsten.  Fluorite  has  been  reported,  and  is  possibly  locally 
present  in  very  minute  grains  in  both  the  hornstone  and  silici- 


76  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

fled  dike  rock,  but  it  has  not  been  possible  to  isolate  it.  Minute 
hollow  cubes  may  have  contained  fluorite,  and  a rare  isotropic 
grain  in  the  gangue  materials  may  be  fluorite.  Ferberite  is 
found  with  the  telluride  ore  in  the  Graphic  mine  at  Magnolia, 
and  a mine  near  Sunshine  shows  sylvanite  associated  with  fer- 
berite. The  Wheelmen  Tunnel — driven  for  gold — shows  both 
ferberite  and  sylvanite.  While  the  relative  age  of  the  ferberite 
and  sylvanite  is  not  always  clear,  specimens  of  the  Magnolia  ore 
leave  little  doubt  that  so  far  as  the  occurrences  there  are  con- 
cerned, the  telluride  is  older.  Porous  quartz  contains  a sprink- 
ling of  sylvanite  well  below  the  surface,  while  a crust  of  drusy 
ferberite  covers  the  surface.  The  ferberite  contains  no  telluride. 
The  relations  in  the  Wheelmen  Tunnel  appear  to  be  much  the 
same.  Secondary  feldspar  having  the  form  and  appearance  of 
adularia  occurs  in  groups  of  tabular  and  prismatic  crystals  in  a 
few  places. 

MINING. 

In  the  early  days  of  tungsten  mining  in  Boulder  County 
open  pits  and  trenches  were  numerous,  and  in  places  “gopher 
mining”  for  float  was  profitable.  At  present  the  larger  mines 
are  well-equipped  and  well  managed.  Leasing  is  very  common, 
especially  on  those  tracts  held  under  homestead  entries.  In 
many  instances  this  method  has  proved  profitable  to  both  owner 
and  leaser. 

CONCENTRATION. 

Mills:  There  are  five  mills  in  the  district  for  the  treatment 
of  tungsten  ores.  With  one  exception  these  are  partially  or 
wholly  made-over  gold  and  silver  mills.  Experimenting  in  va- 
rious lines  has  suggested  many  modifications  and  improvements, 
and  several  of  the  mills  have  reached  a creditable  degree  of 
efficiency  considering  the  difficult  character  of  the  tung- 
sten ores.  The  Wolf  Tongue  mill  at  Nederland  has  treated  the 
Company’s  own  ores  and  has  of  late  been  the  largest  handler  of 
custom  work.  The  Cardinal  mill  at  Cardinal  has  treated  mainly 
the  ores  of  the  Cardinal  Company.  The  Clarasdorf  mill,  below 
Nederland,  was  built  by  the  Philipp  Bauer  Company  to  treat 
the  ores  of  the  Rogers  tract  which  they  held  under  lease.  The 
Primes  mill  at  Primos  in  the  northeastern  area  has  handled  the 
Stein-Boericke  production  and  a good  deal  of  custom  ore.  The 
Lehigh  Tungsten  Mining  and  Milling  Company  has  remodeled 
the  old  Coburn  mill  on  Boulder  Creek,  but  it  has  not  yet  treated 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


77 


PLATE  X. 


Primos  Mill,  Primos. 


Cardinal  Mill,  Cardinal. 


78 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY 


PLATE  XI. 


Wolf  Tongue  Mill,  Nederland. 


Clarasdorf  Mill. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  79 

much  ore.  The  Boyd  mill  in  Boulder  was  used  by  the  Colorado 
Tungsten  Corporation,  both  for  its  own  and  for  custom  ores. 
A few  hundred  tons  of  ores  have  been  treated  by  Henry  E. 
Wood  at  his  plant  in  Denver,  and  other  mills  have  treated  small 
quantities  from  time  to  time. 

Difficulties : The  concentration  of  the  Boulder  County  ores 
presents  some  difficult  problems.  Ferberite  is  a rather  soft  min- 
eral with  one  perfect  cleavage,  and  generally  one  or  more  prom- 
inent partings.  As  a result  the  mineral  is  extremely  friable  even 
in  the  massive  and  massive-granular  forms.  Much  of  the  fer- 
berite was  deposited  as  aggregates  of  loosely  arranged  crystals 
and  crystal  grains,  forming  crusts  over  the  surfaces  of  rock 
fragments.  One  crust  succeeded  another  until  in  many  places 
the  opening  was  filled.  In  other  places  the  cavities  remained 
open,  but  the  walls  were  lined  in  the  same  manner.  The  crystal 
grains  composing  these  crusts  average  not  more  than  one-eighth 
of  an  inch  in  length  and  about  one-sixteenth  of  an  inch  in  dia- 
meter. In  much  of  the  ore  where  the  crust  is  broken  the  crystal 
grains  are  easily  separated  from  one  another.  When  to  this 
ready  crumbling  of  the  mass  is  added  the  extreme  friability  of 
the  grains  and  crystals  themselves,  it  is  easy  to  understand  the 
excessive  sliming.  The  finer  parts  of  the  slimes  form  an  almost 
impalpable  mass  which  when  stirred  in  water  gives  it  an  inky 
appearance,  and  the  water  remains  turbid  for  ten  days  to 
two  weeks.  To  save  these  slimes  is  one  of  the  difficult  problems 
with  which  the  tungsten  mill-man  has  to  contend.  As  a result  of 
the  metallurgical  methods  now  used  in  the  preparation  of  metallic 
tungsten  and  ferro-tungstens,  there  seems  to  be  but  a limited  de- 
mand for  non-concentrated  high  grade  ore.  This  makes  it  necessary 
to  concentrate  even  the  high  grade  ore,  and  consequently  adds  to 
the  loss,  by  disproportionately  increasing  the  slimes.  The  Primos 
Mining  and  Milling  Company  (formerly  the  Stein-Boericke  and 
Cardinal  Companies)  sorts  rather  carefully,  sacks  and  ships  ores 
running  twenty-five  per  cent,  or  over,  and  the  Wolf  Tongue  Com- 
pany ships  ores  exceeding  thirty-five  per  cent,  of  tungstic  oxide, 
but  other  producers  have  not  been  so  favorably  situated  in  this 
respect. 

Another  difficult  problem  is  the  successful  treatment  of  the 
highly  siliceous  ores.  In  almost  all  the  tungsten  mines,  there  is 
a certain  amount  of  highly  siliceous  ore  consisting  of  minute 
grains  of  ferberite  in  a matrix  of  chalcedonic  quartz  or  hornstone. 
The  percentage  of  ferberite  varies  widely.  Outside  of  certain 


80  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

limited  areas  this  type  of  ore  is  fortunately  not  very  abundant, 
and  rarely  amounts  to  twenty  per  cent,  of  the  product.  Various 
methods  of  treatment  have  been  tried,  but  none  has  given  en- 
tirely satisfactory  results.  Even  very  fine  crushing  leaves  a large 
part  of  the  ferberite  with  particles  of  quartz  attached.  In  con- 
centrating, these  grains  consisting  of  quartz  and  ferberite  will 
be  disposed  of  according  to  their  specific  gravity.  Those  in  which 
the  quaitz  is  largely  in  excess  will  go  with  the  tailings  and  fer- 
berite will  be  lost,  and  those  in  which  the  ferberite  is  abundant 
will  go  with  the  concentrates  and  help  to  make  a low  grade 
product. 

In  discussing  with  the  mill-men  the  methods  of  concentra- 
tion best  suited  to  the  ferberite  ores,  a number  of  questions  have 
arisen.  Some  of  these  are  as  follows : 

(1)  Is  the  stamp  mill  the  best  means  of  crushing  the  ores? 

(2)  Would  coarse  crushing  the  unsorted  ore,  jigging  and 
regrinding  (or  stamping)  the  tailings  pay? 

(3)  Would  close  sorting  and  separate  treatment  of  the 
higher  grade  ores  result  in  an  increased  saving  which  would  pay 
the  extra  cost? 

(4)  Would  chemical  treatment  of  the  low  grade  and  the 
highly  siliceous  ores  be  feasible? 

(5)  If  direct  chemical  treatment  of  the  low  grade  and 
highly  siliceous  ores  is  not  feasible,  would  it  be  possible  to  treat 
a low  grade  concentrate  from  them? 

(6)  Is  magnetic  separation  feasible? 

The  writer  does  not  pretend  to  be  a mill-man,  and  his  ob- 
servations have  not  the  backing  of  practical  experience.  But  a 
few  things  are  certain.  Ferberite  is  exceedingly  friable,  and  a 
large  proportion  of  the  particles  into  which  it  breaks  are  thin  and 
flat — the  best  possible  form  to  remain  a long  time  in  suspension 
whether  on  the  tables  or  in  settling  tanks.  Its  friable  character 
is  responsible  for  unavoidable  sliming,  and  its  high  specific  grav- 
ity tends  to  keep  it  longer  in  the  mortar,  and  to  bring  it  under 
the  stamps  more  frequently.  The  vertical  screens  in  use  are  un- 
favorable for  the  quick  escape  of  the  pulp.  The  result  is  that  a 
large  part  of  the  ore  is  reduced  to  a very  fine  slime.  Again,  much 
of  the  gangue  is  hornstone  and  highly  silicified  country  rock 
which  are  anything  but  friable,  and  are  not  readily  crushed  to 
pass  the  screen.  The  rock  grains  aid  in  reducing  the  ore  and  so 
increase  sliming. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  81 

Various  tests  of  concentrates  have  shown  the  extreme  fine- 
ness to  which  the  ferberite  is-  reduced.  The  following  are  given 
as  examples,  and  they  do  not  differ  in  any  important  way  from 
the  average  results : 

a Sample  of  4 pounds  from  Wilfley  tables: 

58.57  % passed  a 150-mesh  sieve. 

77.14%  “ “100-mesh  “ 

82.85%  “ “ 70-mesh 

94.28%  “ “ 40-mesh 

99.28%  “ 20-mesh  “ 

The  discharge  from  the  stamps  in  this  mill  was  through  a 
vertical  12-mesh  screen.  The  sample  did  not  contain  the  saving 
from  special  slimers  or  from  stationary  canvas. 

b Sample  of  3 pounds  of  mixed  concentrates : 

59.4%  passed  a 150-mesh  sieve. 

78.9%  “ “ 100-mesh  “ 

83.0%  “ 70-mesh 

94.1%  “ “ 40-mesh 

99.2%  “ “ 20-mesh 

A few  ounces  of  clean  concentrates  which  passed  a 100-mesh 
screen  were  thoroughly  shaken  up  in  a gallon  bottle  of  water 
and  the  bottle  was  allowed  to  stand.  At  the  end  of  two  weeks 
the  water  was  still  turbid,  and  when  filtered  yielded  a percepti- 
ble amount  of  ferberite  slime. 

A method  of  crushing  by  which  the  fines  would  be  at  once 
screened  out  and  carried  beyond  the  reach  of  the  machine  would 
prevent  a large  part  of  the  sliming.  If  the  stamp  mill  is  used, 
inclined  screens  would  aid  in  this.  The  ferberite  ores  are  in 
several  respects  similar  to  the  zinc  and  lead  ores  of  the  Joplin 
District.  Ferberite  is  probably  a little  more  friable  than  galena. 
Much  of  the  gangue  of  the  Joplin  galena  (and  zinc  blende)  is 
chert,  and  therefore  very  similar  to  the  more  siliceous  gangue 
of  the  ferberite.  The  Joplin  method  of  coarse  crushing  by  means 
of  a Blake  (or  similar  machine),  then  screening,  and  roll-crush- 
ing the  oversize  and  jigging  the  entire  product  removes  at  once 
a very  large  proportion  of  the  values  and  correspondingly  reduces 
sliming.  This  would  be  equally  true  of  the  tungsten  ores.  The 
tailings  could  be  reground  to  the  size  made  necessary  by  their 
character.  But  this  also  should  be  done  in  a mill  which  would 
at  once  release  the  fines. 


82 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Separate  treatment  of  the  high  grade  ores  would  undoubtedly 
i educe  sliming,  since  a very  large  part  of  the  values  could  be 
lemoved  after  coarse  crushing. 

The  chemical  method  of  treatment  is  as  follows:  The  pul- 
verized ore  or  concentrate  is  mixed  with  soda  ash  and  fused. 
Under  proper  conditions  a sodium  tungstate  is  formed  and  the 
extraction  is  complete.  The  mass  is  dissolved  in  water  and  sep- 
arated by  filtration  from  the  oxides  of  iron,  aluminum,  mangan- 
ese and  silicon.  The  addition  of  hot  acid  in  excess  precipitates 
tungstic  acid,  H2W04,  which  separates  as  a yellow  powder.  This 
is  washed  from  soda  salts,  and  dried.  In  drying,  water  is  given 
off  and  tungstic  oxide,  W03,  remains. 

So  far  as  the  composition  of  the  Boulder  county  ores  is 
concerned,  there  is  nothing  to  complicate  the  process,  but  to 
treat  the  raw  ore  in  this  way  would  require  a very  large  amount 
of  soda  ash.  A low  grade  concentrate  could  be  formed  from  the 
ore,  and  this  could  be  treated  more  cheaply.  Highly  siliceous 
concentrates  and  ores  are  treated  by  this  method  in  Europe. 

The  magnetic  separator  is  successfully  used  on  the  complex 
tin-tungsten  ores  of  Cornwall.  There  should  be  no  great  diffi- 
culty in  applying  this  to  the  simple  Boulder  county  ores,  which 
contain  practically  no  metallic  mineral  except  the  ferberite.  Mr. 
Henry  E.  Wood  has  successfully  applied  this  method,  but  regards 
it  as  better  suited  to  the  treatment  of  water-made  concentrates 
than  to  the  treatment  of  raw  ore.  Tests  made  for  the  writer  on 
ores  from  Gordon  Gulch  and  Boulder  Falls  showed  a very  per- 
fect separation  of  material  rejected  by  a 60-mesh  screen.  But 
with  the  pulp  which  passed  the  60-mesh  screen,  the  separation 
was  not  so  perfect — rock  powder  came  over  with  the  ferberite. 
Coarse  crushing  would  seem  to  be  desirable  for  this  method  also. 

The  methods  of  concentration  in  use  in  the  tungsten  field 
are  illustrated  by  the  following  examples : 

1.  The  Boulder  County  Mill  of  the  Primos  Mining  and  Mill - 
ing  Company:  The  ore  that  passes  1 1 "-grizzlies  goes  to  the  stamp 
feed  bin,  while  the  over-size  goes  to  a Blake  crusher,  and  from 
this  to  the  feed  bin.  The  stamps  weigh  750  pounds  and  have  a 
drop  of  6 inches  seventy  times  per  minute.  The  pulp  passes  from 
the  mortar  by  a 12-mesh  screen  and  is  conveyed  to  Wilfley  tables 
which  recover  about  70  per  cent,  of  the  total  saving.  The  over- 
flow goes  to  classifiers  which  make  three  sizes  and  pulp.  The 
coarsest  goes  to  a Frue  vanner  with  a corrugated  belt;  the 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


83 


middlings  and  fine  go  to  Frue  vanners  with  smooth  belts.  The 
overflow  from  the  last  two  tables  goes  by  pump  to  a V-shaped 
settler,  from  which  the  pulp  is  delivered  to  four  Frue  vanners 
with  eggshell  belts.  The  overflow  from  these  goes  to  stationary 
canvas  tables  12'  by  40'  with  a slope  of  1 to  12,  and  from  these  to 
another  set  of  the  same  form  and  size.  The  sand  from  the  corru- 
gated Frue  vanner  goes  to  a Huntington  mill,  where  it  is  re- 
ground to  pass  a 60-mesh  sieve  and  is  delivered  to  the  canvas 
tables. 

2.  The  Clarasdorf  mill  of  the  Phillips  Bauer  Co.:  The  ore 
goes  to  a Traylor  crusher,  from  which  it  falls  onto  a 16-mesh 
screen.  From  this  point  it  is  a wet  process.  The  over-size 
passes  through  a Hodge  crusher,  then  to  rolls,  and  the  product 
returns  to  the  screen.  The  pulp  from  the  screen  goes  to  the  first 
Wilfley  table,  and  the  oversize  returns  to  the  rolls.  The  tailings 
from  that  part  of  the  table  nearest  the  concentrates  are  re- 
ground in  triplex  rolls  to  pass  a 40-mesh  screen,  and  with  the 
overflow  from  the  Wilfley  pass  to  a Traylor  classifier,  which 
makes  four  products.  The  coarsest — mainly  about  40-mesh — goes 
to  the  second  Wilfley,  the  intermediate — mainly  about  60-mesh — 
to  the  third,  and  the  finest — mainly  about  80-mesh — to  the  fourth 
Wilfley.  The  slimes  are  treated  on  two  Traylor  slimers. 

3.  The  Colorado  Tungsten  Corporation's  mill  (the  Boyd 
Mill,  Boulder) : The  equipment  consists  of : A jaw  crusher,  ten 
1,000-pound  stamps,  four  standard  Wilfley  tables,  two  Wilfley 
slime  tables,  eight  Monell  slime  tables,  and  stationary  canvas. 
The  mines  of  the  company  furnished  ores  of  two  rather  distinct 
types.  For  one  of  these  a 16-mesh  screen  was  used,  and  for  the 
other  a 20-mesh  screen. 

The  pulp  was  classified  and  passed  to  the  four  standard 
tables.  The  coarse  tailing  from  the  first  table,  carrying  about 
0.4  per  cent,  of  tungstic  oxide,  was  discarded.  The  tailings  from 
the  second  table  were  reground.  The  tailings  from  the  third  and 
fourth  tables,  mixed,  went  to  four  Monell  tables.  The  tailing 
from  these  went  to  a settling  spitzkasten,  from  which  the  coarse 
material  went  to  two  more  slime  tables,  and  the  slime  to  the 
stationary  canvas.  The  tailings  from  the  last  two  tables  went 
tc  another  large  settling  and  sizing  spitzkasten,  from  which  the 
finer  deposit  went  to  two  or  more  slime  tables,  and  the  overflow 
to  the  stationary  canvas.  There  were  many  changes,  from  time 


84 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


to  time,  in  the  methods  of  classification  and  distribution,  but 
the  above  is  the  plan  during  the  last  month’s  operation. 

The  mill  'practice  of  the  At olia  Mining  Company,  San.  Ber- 
nardino Co.,  Cal.,  working  on  scheelite  ore,  is  as  follows:  The 
ore  is  fed  into  a Blake  crusher,  from  which  it  passes  by  an  auto- 
matic feeder  into  a Huntington  mill  and  is  crushed  to  20-mesh. 
It  then  passes  to  Frue  vanners.  The  high-grade  ore  is  sorted, 
cobbed  and  sacked.  (125r).  . : 

Australian  method:  Stamp  crushing  is  used  at  Koorboora 
on  wolframite  ore  running  4 per  cent.,  but  the  Huntington  mill 
is  more  generally  used  (1906),  and  it  is  believed  that  it  causes 
less  sliming. 

Cornish  tungsten  ore  dressing:  At  the  East  Pool,  Clitters 
and  South  Crofty  mines,  all  of  which  are  relatively  rich  in  wolf- 
ramite, magnetic  separators  have  been  installed  to  remove  the 
wolframite.  The  East  Pool  ore  carries  cassiterite,  arsenopyrite, 
wolframite,  and  chalcopyrite  so  evenly  distributed  in  the  veins 
as  to  make  hand  sorting  impossible.  The  pulp  from  the  stamps 
is  classified  into  sands  and  slimes.  The  sands  go  to  Frue  van- 
ners or  to  Wilfley  tables  (preferably  the  latter  on  account  of 
their  greater  speed) . The  concentrates  contain  the  tin  ore,  wolf- 
ramite and  arsenopyrite,  while  a middling  product  contains  the 
chalcoprite  and  some  tin  ore.  After  being  calcined  to  remove 
the  arsenic,  the  concentrates  are  classified,  and  the  sands  are 
passed  over  Wilfleys  which  yield  a product  containing  about 
three  ports  of  tin  ore  to  one  of  wolframite,  and  about  five  per 
cent,  of  iron  oxide. 

The  slimes  from  the  first  classifiers  go  to  rag  frames  and 
the  product  of  these  passes  over  Acme  tables,  from  which  the 
concentrates  go  to  the  calciner.  The  calcined  residues  pass  over 
Acme  tables.  These  concentrates  and  those  from  the  sand  are 
leached  with  sulphuric  acid,  washed,  dried,  and  passed  through 
a Humboldt- Wether  ill  magnetic  separator  where  a conveyor  belt 
carries  the  material  under  a magnet  strong  enough  to  remove  the 
iron  oxide,  but  too  weak  to  affect  the  wolframite.  The  remain- 
der, containing  tin  ore  and  tungsten  ore,  passes  on  to  a stronger 
magnet  which  removes  the  wolframite.  The  tin  ore  and  other 
ronmagnetic  materials  are  left.  The  object  of  the  sulphuric 
acid  leaching  is  to  prevent  tin  ore  from  adhering  to  the  wolfra- 
mite and  passing  into  the  tungsten  concentrates  in  the  magnetic 
separator.  - r - • — 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


85 


The  Elmore  vacuum  process  has  been  installed  at  the  Dol- 
coath  mine,  but  the  ores  contain  very  little  tungsten. 

Sale  of  ore  and  concentrates : The  concentrates  (and  high- 
grade  ores)  are  sold  by  the  “unit”  of  tungstic  oxide,  which  is 
one  per.  cent,  of  a short  ton,  or  20  pounds.  At  present  the  stand- 
ard concentrate  carries  60  per  cent,  of  tungstic  oxide  (commonly 
called  “tungstic  acid”),  and  must  not  exceed  0.25  per  cent,  phos- 
phorus, nor  0.01  per  cent,  sulphur.  Concentrates  falling  below 
this  standard  are  penalized  a few  cents  for  each  per  cent,  they 
fall  below  this  figure  in  tungstic  oxide,  and  for  any  excess  of 
phosphorus  or  sulphur.  A bonus  is  sometimes  allowed  on  con- 
centrates carrying  over  60  per  cent,  of  tungstic  oxide. 

POSSIBLE  EXTENSION  OF  THE  AREA. 

Rocks  of  the  same  types,  and  in  the  same  relationship  as 
those  of  the  tungsten  area  occur  far  to  the  north  and  to  the  south. 
To  the  north,  however,  there  is  a gradual  increase  in  the  meta- 
morphic  structures  such  as  the  gneissoid  and  schistose  which, 
when  pronounced,  seem  to  be  unfavorable  to  tungsten  deposition. 
To  the  south,  in  Gilpin  county,  granites  and  gneissoid  granites 
prevail  for  some  distance,  and  are  cut  by  pegmatite  and  granite 
dikes  of  the  same  type  as  those  of  the  known  tungsten  area.  While 
the  gold  and  silver  deposits  and  the  tungsten  deposits  are  not  inti- 
mately associated,  the  two  seem  to  conform  roughly  to  the  trend  of 
the  belt  of  intruded  porphyries  which  extends  from  the  middle  of 
Boulder  County  in  a southwesterly  direction  into  Gilpin,  Clear 
Creek,  Summit  and  Lake  counties.  Tungsten  is  known  within 
this  belt  in  Boulder,  Gilpin  and  Clear  Creek  counties. 

Future  of  the  district:  The  present  development  offers  but 
few  data  on  which  to  base  opinions  as  to  the  future  of  the  de- 
posits. The  workings  are  shallow,  the  ore  is  distributed  along 
the  veins  in  bunches  and  pockets  or  rarely  shoots,  and  up  to  the 
present  nothing  has  occurred  to  suggest  that  the  downward 
distribution  is  less  regular  than  the  lateral.  In  fact,  a consid- 
erable number  of  the  best  ore  bodies  have  had  greater  vertical 
than  lateral  dimensions.  This  is  natural  when  it  is  remembered 
that  the  deposition  took  place  from  uprising  solutions,  and  not 
from  solutions  moving  mainly  in  a horizontal  direction.  The 
deepest  workings  in  the  camp  are  showing  ore  bodies  of  dimen- 
sions and  quality  quite  equal  to  those  of  any  yet  discovered. 


86 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


PRODUCTION. 

The  preparation  of  a satisfactory  statement  of  the  produc- 
tion of  the  district  has  proved  a very  difficult  task,  but  the  pro- 
ducers have  very  kindly  placed  their  mining  and  milling  records 
at  the  disposal  of  the  Survey.  These  have  been  compared,  check- 
ed and  arranged,  and  it  is  believed  that  the  following  table  is 
reasonably  accurate: 

Average  price 


1900 

High-grade  ore,  63%  W03 

Tons. 

40 

per  unit. 
$1.30 

Value. 

$ 3,216.00 

1901 

High-grade  ore  and  cencentrates, 
averaging  65%  WO 

65 

2.25 

8,775.00 

1 902 

Ores  and  concentrates 

166 

2.50 

24,900.00 

1903 

Mainly  concentrates 

243 

2.50 

36,317.00 

1 904 

Ores  and  concentrates,  averaging 
about  55%  WO 

375 

5.50 

125,000.00 

1905 

Mainly  concentrates 

642 

6.00 

231,120.00 

1906 

Mainly  concentrates 

789 

6.0  x 

309,603.00 

1907 

Mainly  concentrates 

1,146 

8.33 

573,643.00 

j 908 

( High-grade  ore  180  ) 

( Concentrates  407  j 

587 

— 

164,220.00 

MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


87 


CHAPTER  III— TECHNOLOGY  AND  USES  OF  TUNGSTEN. 


THE  METAL  AND  ITS  METALLURGY. 

The  metal:  There  is  still  a notable  lack  of  agreement  among 
chemists  regarding  the  propeities  of  tungsten.  The  statements 
following  are  compiled  from  the  latest  publications.  Metallic 
tungsten  is  generally  produced  in  the  foim  of  a black  or  gray- 
ish-black powder.  The  fused  metal  is  slightly  darker  than 
metallic  zinc,  and  is  distinctly  lustrous.  It  is  brittle,  and  non- 
ductile  (some  say  ductile  and  malleable),  but  may  be  welded, 
filed  and  forged.  Sulphuric  and  hydrochloric  acids  attack  it 
slowly,  nitric  moie  vigorously,  and  a mixture  of  nitric  and  hydro- 
fluoric acids  readily  dissolves  it.  Aqua  legia  oxidizes  the  powder 
form,  but  does  not  act  upon  the  fuser  metal.  Under  ordinary 
atmospheric  conditions  it  is  veiy  slcwiy  oxidized,  but  at  red  heat 
it  is  rapidly  changed  to  tungstic  oxide.  The  fused  metal  has  a 
specific  gravity  variously  estimated  from  16  6 (Stavenhagen) , to 
18.7  (Moissan) , and  19.13  (Remsen) . The  melting  point  is  placed 
at  2,800°  C.  by  Wartenberg,  but  as  high  as  3,080°  C.  by  Waidner 
and  Burgess  of  the  Bureau  of  Standards,  Washington. 

Metallurgy  of  tungsten:  The  following  three  examples  may 
be  regarded  as  representing  the  methods  of  obtaining  tungsten 
from  its  ores : I.  The  ore  is  ground  to  pass  an  eight  or  ten- 
mesh  sieve,  and  is  brought  to  a cherry-red  heat  and  fused  with 
sodium  carbonate  (soda-ash).  The  sodium  tungstate  thus  formed 
is  dissolved  in  boiling  water,  filtered  from  the  solid  impurities, 
and  treated  with  hot  hydrochloric  acid  (or  nitric),  in  earthen 
vessels.  This  precipitates  tungstic  acid,  H2W04.  The  liquid  is 
drawn  off  and  the  tungstic  acid  is  washed  to  remove  sodium 
salts,  and  is  then  converted  into  tungstic  oxide  by  drying.  The 
dry  oxide  is  mixed  with  pure  carbon  and  placed  in  crucibles  and 
heated  to  a very  high  temperature  in  a gas  furnace.  The  carbon 
and  the  oxygen  of  the  ore  unite  and  pass  off,  leaving  a black  or 
gray-black  metallic  powder,  which  usually  contains  a small 
amount  of  carbon. 

2.  The  tungstic  oxide  is  produced  by  the  same  method,  but 
the  reduction  with  carbon  is  effected  in  an  electric  furnace.  This 
method  is  said  to  produce  a metal  quite  low  in  carbon. 


88  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

3.  The  pulverized  ore  is  mixed  with  pure  carbon  or  placed 
in  carbon-lined  crucibles,  and  reduced  in  an  electric  furnace.  The 
impurities,  chiefly  iron  and  manganese,  and  the  oxygen  unite  with 
the  carbon,  and  metallic  tungsten  is  left. 

Other  methods,  some  of  which  have  been  used  on  a com- 
mercial scale,  are : 

1.  The  tungstic  oxide  is  reduced  in  a current  of  hydrogen, 
which  unites  with  the  oxygen  of  the  oxide,  forming  water  and 
leaving  a black  powder  of  metallic  tungsten. 

2.  The  Goldschmidt  or  alumino-thermite  process : The 
oxide  of  the  metal  is  mixed  with  finely  powdered  aluminum  and 
a readily  ignited  substance  such  as  barium  peroxide,  in  refrac- 
tory crucibles.  The  mass  is  ignited  and  the  intensely  heated 
aluminum  unites  with  the  oxygen  of  the  tungstic  oxide,  and  the 
heat  of  the  reaction  forms  a metallic  bath  in  the  crucible.  The 
aluminum  is  oxidized  to  the  form  of  corundum,  ( A1203) . By  proper 
adjustment  of  the  charge  the  ore  is  completely  reduced  and  the 
aluminum  is  entirely  oxidized.  This  produces  a carbon-free  metal. 

3.  The  tungstic  oxide  is  mixed  with  powdered  zinc  and 
heated  to  redness  until  the  zinc  , is  distilled  off.  The  mass  is 
freed  from  zinc  oxide  by  hydrochloric  acid,  and  from  the  remain- 
ing tungstic  oxide  by  sodium  hydroxide. 

4.  Powdered  tungsten,  powdered  manganese,  tungstic  oxide 
and  manganese  dioxide  are  mixed,  compressed  and  heated  in  a 
stream  of  hydrogen.  A mass  of  tungsten  and  manganese  (not 
strictly  an  alloy)  is  formed,  from  which  the  manganese  is  re- 
moved by  acids. 

5.  Powdered  tungstic  oxide  is  heated  with  one-tenth  its 
weight  of  sugar  charcoal  in  the  electric  furnace.  With  care,  this 
yields  an  almost  carbon-free  metal. 

6.  Tungsten  concentrates  are  reduced  to  lower  oxide  form 
by  means  of  carbon  in  an  electric  furnace.  Silicon  carbide  is 
added  and  the  reduction  is  completed.  (Becket  process.) 

7.  The  Greene  and  Wahl  ferro-silicon  method  has  also  been 
used. 

USES  OF  TUNGSTEN  AND  TUNGSTEN  COMPOUNDS. 

Introduction:  Pure  metallic  tungsten  is  but  little  used  in 
finished  industrial  products.  But,  alloyed  with  other  metals,  and 
in  various  chemical  compounds,  the  use  of  tungsten  has  recently 
become  important.  Many  of  its  physical  and  chemical  proper- 
ties have  been  known  for  decades,  but  until  recently  the  supply 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  89 

of  tungsten  ore  was  so  uncertain  and  irregular  that  there  has 
been  little  inducement  to  develop  industries  dependent  upon  a 
supply  of  tungsten.  The  discovery  of  the  Australian  deposits 
and  those  of  the  U.  S.  has  given  manufacturers  reasonable  as- 
surance that  an  increasing  demand  would  be  met. 

The  certainty  of  a supply  of  ore  encouraged  a more  thorough 
study  of  the  metal  and  its  possible  uses.  And  the  development  of 
the  gas  and  electric  furnaces  for  metallurgical  purposes  made 
the  production  of  metallic  tungsten  much  less  expensive.  As  a 
result,  the  demand  for  tungsten  has  increased  very  rapidly,  and 
the  metal  has  taken  its  place  as  a necessary  factor  in  a number 
of  important  industries. 

Tungsten  is  employed  chiefly  in  the  following  forms : 

The  metal  is  used:  (1),  for  the  making  of  alloys  with  vari- 
ous metals,  such  as  iron,  aluminum,  nickel,  copper,  titanium,  tin 
and  others.  (The  alloys  will  be  discussed  below.)  A small 
amount  of  tungsten  is  mixed  with  the  magnetite  in  the  electrode 
of  the  “magnetite  arc”  lamp ; (2) , for  filaments  in  the  tungsten  in- 
candescent lamp,  and  has  been  tried  as  an  electrode  in  arc  lamps. 

There  are  at  least  a hundred  patents  recorded  for  the  prep- 
aration of  incandescent  lamp  filaments  in  which  tungsten  is  the 
important  metal.  In  most  of  these,  metallic  tungsten  powder 
forms  part  of  a plastic  mass  or  paste,  which  is  made  into  a fila- 
ment by  forcing  it  through  a die  having  an  opening  of  the  re- 
quired size.  The  substances  used  for  the  paste  are  different  in 
the  different  processes,  but  various  gums,  sugar,  syrup  and  other 
viscous  liquids  form  the  binding  materials  with  which  the  me- 
tallic tungsten  powder  and  some  form  of  carbon  are  mixed.  When 
the^  filaments  come  from  the  die  they  are  dried  and  gently  heated 
away  from  air.  They  are  then  ignited  by  an  electric  current  in 
an  atmosphere  of  hydrogen  (or  other  reducing  gas)  and  sufficient 
oxygen  (or  water  vapor)  to  dispose  of  the  carbon.  They  are 
hardened  at  very  high  temperatures. 

The  General  Electric  Company  has  patented  a process  in 
which  the  binding  mass  is  an  alloy  of  42  parts  cadmium,  5 to 
10  parts  of  bismuth  and  53  parts  of  mercury.  With 
35  parts  of  this  alloy  are  mixed  65  parts  of  metallic  tungsten 
and  a refactory  oxide  such  as  that  of  thorium.  The  filaments 
are  finished  by  electrically  heating  them  in  an  atmosphere  of 
hydrogen.  . In  one  process,  metallic  tungsten  is  mixed  with  an 
oxide  of  one  of  the  metals : titanium,  thorium,  zirconium,  or 


90 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


vanadium,  or  with  a mixture  of  the  oxides  of  two  or  more  of 
these.  Filaments  having  a coating  of  tungsten  over  a core  of 
another  metal  have  been  tried,  as  have  also  hollow  filaments 
made  by  coating  a carbon  filament  with  tungsten  in  an  atmos- 
phere consisting  of  a halogen  or  an  oxyhalogen  of  tungsten.  The 
carbon  core  is  removed  by  burning  the  filament  in  an  atmosphere 
containing  nitrogen  and  hydrogen.  A partially  metalized  filament 
is  made  by  packing  carbon  filaments  in  oxides  of  tungsten  and 
heating  them  in  a vacuum  furnace.  The  oxides  are  partially  vapor- 
ized, and  entering  the  carbon,  are  reduced  to  metallic  tungsten. 

The  brittleness  of  the  tungsten  filament  is  probably  due  to 
the  presence  of  a carbide  (or  an  oxide)  of  tungsten.  In  most  of 
the  methods  of  manufacture  there  would  be  little  danger  of  an 
oxide  remaining,  but  the  carbides,  W2C  and  WC  may  be  present 
in  the  metallic  tungsten  powder  used,  and  under  certain  condi- 
tions the  carbide  W2C  may  be  formed  in  the  making  of  the  fila- 
ment. 

It  is  interesting  to  note  that  two  or  more  of  the  large  manu- 
facturers of  incandescent  lamps  specify  that  Boulder  County 
tungsten  must  be  used  in  the  filaments.  Most  of  the  foreign 
tungsten  deposits  are  associated  with,  or  contain,  minerals  carry- 
ing one  or  more  of  the  following  elements : sulphur,  phosphorus, 
tin,  arsenic  and  antimony,  all  of  which  render  the  metallurgy 
more  complex,  and  make  the  production  of  a pure  metallic  tung- 
sten more  difficult.  Even  a small  trace  of  sulphur,  phosphorus, 
tin  or  arsenic  is  said  to  be  very  detrimental  to  the  filament,  and 
it  is  very  reasonable  to  suppose  that  sulphur  and  phosphorus 
are  as  objectionable  in  ferrotungsten  and  tungsten  steel  as  they 
are  in  ordinary  steel.  Probably  the  only  foreign  tungsten  de- 
posits which  compare  in  purity  with  the  Boulder  County  ores 
are  those  of  Saxony  and  Bohemia. 

Some  of  the  claims  made  for  the  tungsten  filament  are: 
brilliant  white  light ; increasing  resistance  with  increasing  heat ; 
an  efficiency  of  1 to  1.2  watts  per  (Hefner) candle  power;  (the 
ordinary  carbon  lamp  uses  from  3.5  to  4.  watts  per  candle  pow- 
er) ; an  average  efficient  life  of  1,000  hours;  that  it  is  but  little 
affected  by  irregularity  of  voltage.  (116.) 

Tungstic  oxide,  W03,  has  but  few  direct  commercial  uses. 
Certain  metallurgical  processes  for  the  production  of  metallic 
tungsten,  ferrotungsten,  tungsten  steel  and  other  alloys,  may  be 
said  to  start  with  the  tungstic  oxide,  while  in  others,  such  as 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


91 


the  fusion-lixiviation  method,  its  separation  from  the  sodium 
tungstate  is  one  of  the  steps  in  the  process.  It  is  the  essential 
part  of  certain  mordants  used  in  dyeing  textile  materials  and 
fabrics.  It  is  also  used  in  paper  staining  and  printing.  But  in 
both  these  uses  a tungstate  (usually  the  sodium  paratungstate) , 
is  used  as  a source  of  the  oxide,  and  it  is  probable  that  tungstic 
acid,  H2W04,  rather  than  the  oxide,  is  the  form  in  which  tung- 
sten takes  part  in  the  reactions.  Sodium-  and  barium-tungstates 
are  used  in  glass-coloring  and  pottery  glazing.  The  colors  ob- 
tained include  various  shades  of  yellow  and  blue. 

The  tungstates  are  the  chief  ores  of  the  metal,  and  are  there- 
fore the  primary  source  of  tungsten  in  whatever  form  it  may  be 
used  in  the  industries.  The  insolubility  (in  water)  limits  the 
direct  use  of  the  natural  tungstates  except  as  sources  of  the 
metal  and  its  commercial  compounds.  Scheelite  is  used  in  the 
Roentgen  ray  fluoroscope.  Tungsten  forms  soluble  tungstates 
with  sodium  and  potassium.  Those  of  sodium  are  by  far  the 
most  important,  and  are  made  by  fusing  powdered' wolframite, 
hubnerite  or  ferberite  with  sodium  carbonate.  Sodium  paratung- 
state, the  commercial  sodium  tungstate,  NaioWi204i.28H20,  is 
the  most  important  artificial  tungstate.  It  is  used  as  a mordant 
in  dyeing  and  calico  printing,  and  for  rendering  vegetable  fibers 
and  fabrics  uninflammable.  Sodium  tungstate  and  other  tungsten 
compounds  characterized  by  rich  color  tones  are  used  in  the  man- 
ufacture of  stained  papers.  Tungsten  salts  are  also  used  for 
weighting  silk  fabrics. 

The  partial  decomposition  of  the  sodium  and  potassium  tung- 
states yields  a series  of  tungsten  bronzes  of  very  beautiful  colors 
and  high  lusters.  A fusion  of  potassium  tungstate  and  tin  yields 
“bronze  powder.”  These  tungsten  bronzes  and  bronze  powder 
are  much  used  for  decorating.  Lead  tungstate  was  sometimes 
substituted  for  white  lead  as  a pigment. 

ALLOYS  OF  TUNGSTEN. 

Various  alloys:  Tungsten  forms  useful  alloys  with  many 
metals.  It  unites  in  almost  any  proportions  with  iron  and  steel. 
(The  iron  and  steel  alloys  will  be  discussed  more  fully  below.) 

Platinoid  contains  copper,  zinc,  nickel  and  a small  percent- 
age of  tungsten.  Its  high  electrical  resistance  does  not  decrease 
with  heat.  “Wolfram-aluminum”  is  a very  useful  alloy,  which 
may  be  rolled,  spun  and  woven.  It  is  used  for  military  appli- 
ances. A light  and  very  strong  alloy  of  tungsten  and  aluminum, 


92 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


called  partinium,  is  used  in  automobile  manufacture.  An  alloy 
of  tungsten,  aluminum  and  copper,  having  great  tensile  strength 
and  elasticity,  is  used  for  propeller  blades.  Sideraphite  con- 
tains much  iron,  with  nickel,  aluminum,  copper  and  4 per  cent, 
of  tungsten.  It  is  malleable,  ductile,  and  resists  acids.  Minar- 
gent  is  an  alloy  of  tungsten,  nickel  and  copper.  An  alloy  con- 
taining 73-75%  tungsten,  23-25%  nickel,  a small  amount  of  iron, 
carbon  and  silicon  finds  a ready  market.  The  so-called  alloys 
with  manganese  are  unstable,  and  are  probably  not  true  alloys, 
since  the  manganese  can  be  dissolved  out,  leaving  a tungsten  web 
or  network.  There  are  several  alloys  with  iron  and  nickel ; with 
nickel  alone,  and  with  iron  and  chromium.  Alloys  of  tungsten 
and  titanium  and  tungsten  and  zirconium  have  been  used  with 
good  success  as  filaments  for  incandescent  lamps.  Alloys  of 
tungsten,  with  copper  and  iron;  iron,  copper  and  aluminum; 
iron,  titanium  and  carbon ; iron,  columbium  and  tantalum,  are 
available. 

Carbides  of  tungsten  and  chromium  are  extremely  hard,  and 
resist  acids  well. 

Iron  and  steel  alloys:  The  alloys  of  tungsten  with  iron 
and  steel  are  by  far  the  most  important.  Those  with  iron  are 
known  as  ferro-tungstens,  and  ferro-alloys.  Their  chief  use  is  in 
the  manufacture  of  tungsten  steels.  Those  with  steel  are  known 
as  tungsten  steel,  wolfram  steel,  high-speed  steel. 

Ferro-tungsten:  The  ferro-tungstens  commonly  carry  from 
30  to  85  per  cent,  of  tungsten.  They  are  sometimes  classed  ac- 
cording to  the  percentages  of  carbon  and  tungsten  into : a,  high 
carbon  and  medium  tungsten ; b,  high  carbon  and  high  tungsten ; 
c,  low.  carbon  and  high  tungsten.  Those  having  the  higher  per- 
centages of  tungsten  are  favored.  The  following  are  typical : 


w Fe  C 

1  60.92  28.38 

2  83.90  12.10  3.30 

3  ____  78.80  10.90  3.20 

4  84.30  14.90  .72 

5  85.79  13.50  .60 

6  85.15  14.12  .45 

7  71.80  24.35  2.58  Mn.  78 


The  temperature  required  for  the  making  of  ferro-tungsten 
cannot  be  reached  in  the  blast  furnace.  There  are  several  meth- 
ods of  manufacture  in  use : 1.  The  direct  reduction  of  the  tung- 
sten concentrates  (with  scrap  iron,  or  iron  ore  if  necessary)  in 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  93 

a Moissan  or  other  electric  furnace;  2.  The  Rossi  method,  which 
combines  the  electric  furnace  and  a modified  aluminum  process. 
A graphite-lined  furnace  is  so  arranged  that  the  lining  becomes 
the  cathode,  and  a carbon  electrode  dipping  into  the  furnace 
cavity  forms  the  anode.  Scrap  or  bar  aluminum  is  charged  into 
the  furnace  and  the  current  turned  on.  The  aluminum  forms  a 
molten  bath  in  which  the  tungsten  concentrates,  consisting  main- 
ly of  FeW04,  (or  FeO.WOa),  are  placed.  The  iron  oxide  is  re- 
duced to  a metallic  bath  in  which  the  tungsten  dissolves.  The 
aluminum  takes  up  the  oxygen  of  the  concentrates,  forming  a 
slag  on  the  surface  of  the  molten  ferro-tungsten.  This  produces 
an  alloy  low  in  carbon.  3.  The  crushed  ore  or  concentrate  is 
mixed  with  the  proper  amount  of  iron,  either  metallic  or  in  the 
form  of  an  ore,  and  ten  to  fifteen  per  cent,  of  charcoal,  a like 
amount  of  pulverized  quartz,  and  five  per  cent,  of  scrap  glass. 
With  rich  ores  or  concentrates,  a small  percentage  of  resin  or 
pitch  should  be  added.  The  mixture  is  placed  in  graphite  or  clay 
crucibles  and  fused  in  a crucible  furnace,  or  a gas  regenerative 
furnace. 

Tungsten  steel:  The  effect  of  tungsten  as  a steel-hardening 
metal  was  known  as  early  as  1855,  but  it  was  not  until  Robert 
Mushet,  an  English  iron  master,  placed  his  “special  steels”  on 
the  market  a few  years  later,  that  any  commercial  use  was  made 
of  the  knowledge.  The  Mushet  steels  contained  tungsten  in  vary- 
ing percentages  from  6.4  up  to  10.  They  were  known  as  self- 
hardening,  or  air  hardening,  or  high-speed  steels.  It  was  later 
discovered  that  tools  made  of  the  Mushet  steel,  reheated  to  a 
yellow  heat,  and  cooled  in  a current  of  air,  possessed  greater 
hardness  and  greater  cutting-efficiency.  The  Mushet  steels  con- 
tained less  tungsten  and  more  manganese  than  the  average  high- 
speed steel  of  to-day.  The  special  qualities  given  to  steel  by  the 
addition  of  tungsten  depend  upon  a nice  balancing  between  the 
carbon  (manganese)  and  tungsten.  Several  contain  chromium 
also.  With  3%  of  tungsten  and  0.9%  carbon,  the  tenacity  of  the 
steel  reaches  its  maximum,  and  its  ductility  is  not  materially  de- 
creased. As  the  percentage  of  tungsten  rises  from  9 to  16,  the 
steel  becomes  very  hard  and  brittle,  but  its  efficiency  in  cutting 
tools  is  greatly  increased.  Beyond  16%  of  tungsten,  the  steel 
becomes  softer  and  tougher  and  the  cutting  efficiency  decreases. 

Taylor  and  White,  of  Bethlehem,  Pa.,  recommend  the  follow- 
ing steels: 


94 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


W 

Cr 

C 

1.  For 

cutting 

hard  steel__ 

8.5 

4.0 

1.25 

2.  For 

cutting 

soft  steel 

8.5 

3.0 

0.75  to  1.0 

The  analysis  of  one  of  their  best  high-speed  steels,  the  “A. 
W.,”  shows:  Tungsten,  13.5%  ; chromium,  3.5%  ; carbon,  0.55  %. 

H.  M.  Howe  (Iron,  Steel  and  Other  Alloys)  gives  the  follow- 
ing ranges  for  many  of  the  tungsten  steels : 

W 3.44  to  24.00 

Cr 0.00  to  6.00 

C 0.40  to  2.19 

Si 0.21  to  3.00 


Total 4.05  to  35.19 

Nickel  is  also  added  to  some  tungsten  steels. 

In  an  iron-working  machine,  when  a cutter  made  of  hard 
carbon  steel  develops  a temperature,  through  friction,  of  about 
500°  F.,  it  begins  to  lose  its  temper.  This  fact  limits  the  speed 
at  which  the  machine  may  be  run.  The  tungsten  steel  cutters 
do  not  begin  to  soften  until  a temperature  of  1,000°  F.  to  1,200° 
F.  is  passed.  The  tools  are  completely  restored  by  reheating  to 
a very  high  temperature  and  cooling  in  an  air  blast.  They  are, 
therefore,  not  strictly  self-hardening.  It  is  also  found  that  the 
higher  the  temperature  used  in  reheating,  the  higher  may  be  the 
temperature  developed  by  friction  before  the  tool  will  soften. 

The  uses  of  tungsten  steel:  1.  The  tougher  grades  are  be- 
ing used  for  armor  plate,  and  the  harder  for  heavy  projectiles. 
Edge  tools  and  various  other  kinds  are  being  made  of  tungsten 
steel. 

2.  The  harder  grades  are  used  for  cutters  for  steel-  and  iron- 
working machinery. 

3.  Car  springs  of  high  carrying  power  are  made  of  the  more 
elastic  grades.  Tungsten  steel  has  also  been  used  with  excellent 
results  for  railway  frogs  and  rails  in  places  where  the  wear  is 
very  heavy. 

4.  Tungsten  steel  will  retain  a high  degree  of  magnetism 
for  a long  period,  and  is  therefore  used  for  “permanent  magnets/’ 
such  as  compass  needles,  and  calibrating  instruments. 

5.  Sounding  plates  and  wires  for  musical  instruments,  made 
of  tungsten  steel,  give  a more  powerful  response. 

6.  It  is  reported  that  heavy  guns,  car  wheels  and  the  wear- 
ing parts  of  heavy  machinery  are  being  made  of  tungsten  steel. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  95 

7.  An  alloy  containing  35%  tungsten  and  65%  iron  is  used 
for  shells  for  lead  bullets  to  increase  their  penetrating  power. 

Manufacture  of  tungsten  steel:  Probably  the  earliest  method 
of  making  tungsten  steel  was  by  adding  tungstic  oxide  to  the 
molten  steel  in  the  crucible.  Later,  Mushet  mixed  roasted  wol- 
framite with  pitch  and  added  it  to  the  crucible.  The  product 
of  these  methods  would  be  irregular  in  the  percentage  of  tung- 
sten, and  would  be  likely  to  contain  unreduced  tungstic  oxide 
in  damaging  amount.  Then  followed  the  methods  described  be- 
low, and  now  in  use: 

1.  Powdered  metallic  tungsten  is  added  to  the  steel  in  the 
crucible  until  the  desired  percentage  of  tungsten  is  reached. 

2.  Ferro-tungsten  of  known  composition  is  added  in  proper 
amount.  Several  other  processes  have  been  patented,  of  which 
the  following  may  be  regarded  as  a type;  tungsten  concentrates 
(or  ore),  metallic  zinc  and  iron  are  heated  in  an  electric  furnace. 
The  zinc  reduces  the  oxides  of  iron  and  tungsten,  forming  zinc 
oxide,  which  is  carried  away.  (124a). 

The  first  method  is  favored  in  Germany  and  is  largely  used 
in  America.  The  second  method  is  more  used  in  England,  ana 
the  following  reasons  are  advanced  in  its  favor:  The  powdered 
metal  oxidizes  readily  at  red  heat,  and  is  likely  to  carry  tungstic 
oxide  into  the  steel ; the  ferro-tungsten  unites  more  readily  with 
the  steel  and  with  less  loss;  the  powder  is  more  likely  to  carry 
impurities  than  is  the  ferro-tungsten;  the  ferro-alloy  costs  less 
per  unit  of  tungsten  than  does  the  powder.  The  lack  of  uniform- 
ity in  the  earlier  tungsten  steel  is  believed  by  Hadfield,  of  Shef- 
field, to  be  due  to  the  fact  that  more  or  less  oxide  was  intro- 
duced with  metallic  tungsten. 


96 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


SUPPLEMENTAL  REPORT 


EXTENSION  OF  THE  AREA. 

At  the  time  of  writing  the  report  now  reprinted,  tungsten  ore 
had  been  found  at  numerous  points  beyond  the  border  of  the  map 
accompanying  the  report,  but  none  of  these  findings  had  been 
sufficiently  developed  to  justify  the  extension  of  the  mapping  to 
include  them.  Under  the  stimulus  of  the  present  high  prices  these 
bordering  areas  are  being  thoroughly  investigated,  and  abandoned 
prospects  and  low  grade  properties  are  being  converted  into  profit- 
able mines.  The  reports  of  promising  finds  in  Gilpin  county, 
and  the  pushing  of  the  prospected  territory  westward  and  north- 
westward are  very  gratifying.  As  suggested  on  p.  85  there  are  no 
geological  reasons  why  the  tungsten  ores  should  be  confined  to 
the  area  in  which  they  are  now  mined.  It  is  to  be  hoped  that  the 
coming  of  spring  will  witness  very  active,  intelligent  prospecting 
on  all  sides  of  the  known  tungsten  area,  and  in  other  regions  of 
similar  geological  formations  and  structures  elsewhere  in  the 
state.  The  geological  map  of  Colorado  shows  that  formations  and 
structures  similar  to  those  about  Nederland  are  very  widespread. 

Much  of  this  area  has  never  been  prospected  for  tungsten. 
The  fact  that  it  may  have  been  gone  over  for  other  ores  or  other 
metals  is  no  argument  against  thorough  examination  for  tungsten 
ores.  The  known  tungsten  area  is,  in  large  part,  an  old  mining 
region  on  the  surface  of  which  lay  tungsten  float,  but  no  one  was 
sufficiently  interested  in  this  “black  iron”  or  “bastard  silver  ore” 
to  have  it  tested  to  determine  its  real  composition  or  possible 
value. 

TUNGSTEN  IN  OTHER  COUNTRIES. 

The  only  important  producer  to  enter  the  field  since  the  first 
issue  of  the  Report  is  India.  The  occurrence  of  tungsten  in  Tenas- 
serim  and  other  parts  of  Burma  was  mentioned,  but  the  first  re- 
ported production  was  7 tons  in  1909. 

In  1911  India  led  the  world  with  a production  of  1329  metric 
tons,  and  she  has  maintained  her  position  from  that  date.  The 
principal  output  comes  from  Tenasserim  and  the  Southern  Shan 
States.  In  Tenasserim  the  Tavoy  and  Mergin  districts  are  the 
chief  producers.  The  mining  areas  are  hard  to  reach  and  the 
climate  is  very  trying.  The  ore  is  wolframite,  or  possibly  fer- 
berite,  and  occurs  in  both  placer  deposits  and  fissure  veins. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  97 

The  greater  part  of  the  production  comes  from  the  placers 
where  the  ore  occurs  in  lumps  ranging  in  size  from  that  of  a 
marble  to  masses  of  several  pounds.  The  alluvium  containing  the 
ore  is  washed  in  running  water.  The  wolframite  is  picked  out 
by  hand  and  freed  from  rock  and  earth  by  breaking  and  re- 
washing. On  account  of  the  scarcity  of  water  mining  operations 
are  confined  to  about  five  months  in  the  year. 

The  vein  deposits  occur  in  the  mountains  farther  east.  Meta- 
morphic  rocks  derived  from  shales  and  clays  overlie  an  intruded 
granite  which  is  responsible  for  the  metamorphism.  The  veins 
cut  the  metamorphic  rocks  and  pass  down  into  the  granite.  The 
metallic  minerals  of  the  veins  include  pyrite,  arsenopyrite,  cas- 
siterite,  and  wolframite,  (or  possibly  ferberite).  The  principal, 
gangue  is  quartz.  The  veins  have  been  grouped  as : 

1.  Wolframite-quartz  lodes; 

2.  Cassiterite-quartz  lodes; 

3.  Wolframite  greisen. 

The  South  Shan  States  bid  fair  to  rival  or  outstrip  Tenasserim 
as  producers  of  tungsten. 

Portugal  has  maintained  her  place  as  the  largest  European 
producer  of  tungsten.  New  deposits  have  been  opened  in  the  Serra 
da  Estrella  mountains  and  elsewhere  in  the  central  and  northern 
parts  of  the  country.  With  the  exception  of  a part  of  the  ore  from 
Castello  Branca  the  Portugese  tungsten  ores  carry  tin,  and  most 
of  them  are  associated  with  pyrite  and  arsenopyrite. 

Canada  has  become  a small  producer  of  tungsten.  Scheelite 
is  mined  in  Nova  Scotia. 

Japan  produces  between  200  and  300  metric  tons  per  year. 

THE  BOULDER  COUNTY  TUNGSTEN  MINERALS. 

Ferberite:  During  times  of  low  prices  ferberite  finds  a much 
more  ready  market  than  do  the  other  ores  of  tungsten.  This  is 
due  to  the  facts  that  the  principal  ore  of  the  United  States  is  the 
Boulder  County  ferberite,  which  is  very  nearly  free  from  objec- 
tionable impurities,  is  more  easily  smelted  than  any  of  the  other 
ores  especially  in  electric  furnaces,  and  can  be  used  directly.  Hub- 
nerite,  scheelite,  and  to  some  extent  wolframite  require  different 
fluxes  and  the  refiners  prefer  uniformity  of  practise.  At  the  present 
time  when  ferberite  is  selling  as  high  as  $90.00  per  unit  of  tung- 
stic acid  all  the  ores  are  in  demand  though  some  buyers  refuse  the 
highly  manganiferous  hubnerite. 

Scheelite  is  being  found  in  greater  quantity  than  formerly  in 
the  Boulder  area,  but  it  cannot,  as  yet,  be  regarded  as  a factor  in 


98 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


the  production.  It  is  intimately  associated  with  the  country  rock 
and  in  some  instances  clearly  represents  a partial  replacement  of 
it.  It  is  not  likely  to  increase  in  the  deeper  workings. 

Some  specimens  of  scheelite  from  near  Boulder  Falls  appear 
to  be  replacements  of  a porphyritic  dike  rock.  They  retain  the 
porphyritic  texture,  and  except  for  their  high  specific  gravity  may 
be  readily  mistaken  for  weathered  country  rock.  It  is  reported 
that  considerable  quantities  have  been  thrown  aside  as  “heavy 
country  rock/’ 

Hubnerite  has  been  found  in  commercial  quantity  in  only  a 
small  area  between  Black  Tiger  Gulch  and  Boulder  Falls.  At  the 
junction  of  the  Elmettie  vein  with  an  intersecting  vein  from  the 
northwest  a very  large  body  of  hubnerite  was  found.  At  other 
points  along  the  Elmettie  small  amounts  of  this  mineral  occur.  On 
the  outer  borders  of  the  area  in  the  direction  of  Ward,  and  in  the 
Ward  mines  the  tungsten  mineral  is  almost  all  hubnerite. 

Nothing  that  can  be  called  wolframite  is  found  in  appreciable 
quantity  in  Boulder  County. 

Tungstic  ochre,  Tungstite:  Within  the  last  year  several 
specimens  of  ferberite  showing  considerable  coatings,  and  in  one 
or  two  instances  vug  fillings,  of  tungstite  have  been  found.  The 
quantity  of  tungstite  is  far  too  small  to  give  it  any  commercial 
significance.  The  mineral  is  a soft,  earthy,  yellow  to  yellowish  green 
powder  crumbling  under  the  touch,  occasionally  showing  traces 
of  crystal  faces  when  examined  under  a strong  lens.  Its  com- 
position is  W03,  with  tungsten  79.3  per  cent.  It  results  from  the 
alteration  of  ferberite. 

The  yellow  powder  formed  in  the  ordinary  tests  for  tungsten 
is  of  the  same  general  composition,  color  and  properties  as  tung- 
stite, but  is  usually  somewhat  hydrous,  and  in  this  respect  more 
nearly  approaches  meymacite  in  composition.  An  earthy,  kaolin- 
rich  vein  matter  from  near  Magnolia  also  shows  the  presence  of 
tungstite,  but  in  very  limited  amount. 

THE  DARK  TUNGSTEN  MINERALS. 

It  is  a well  recognized  fact  that  there  is  no  natural  subdivision 
of  the  dark  tungsten  series  into  the  three  minerals  hubnerite,  wol- 
framite and  ferberite.  They  form  a series  graduating  from 
almost  pure  manganese  tungstate  at  the  one  end  to  an  almost  pure 
iron  tungstate  at  the  other.  In  the  middle  of  the  series  are  forms 
in  which  the  manganese  tungstate  and  the  iron  tungstate  are 
present  in  almost  equal  amounts.  Hess  has  proposed  the  following 
definitions  for  what  he  calls  the  wolframite  series : 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  99 

“Ferberite:  A monoclinic  iron  tungstate  having  when  pure 
the  composition,  FeW04.  It  may  contain  not  more  than  20  per 
cent  of  the  hubnerite  molecule,  MnW04. 

Hubnerite:  A monoclinic  manganese  tungstate  having  when 
pure  the  composition  MnW04.  It  may  contain  not  more  than  20 
per  cent  of  the  ferberite  molecule,  FeW04. 

Wolframite : A monoclinic  mineral  containing  the  ferberite 
molecule,  (FeW04),  and  the  hubnerite  molecule,  (MnWOJ,  in  all 
proportions  between  20  per  cent  FeW04  and  80  per  cent  MnW04 
and  80  per  cent  FeW04  and  20  per  cent  MnW04.” 

ASSOCIATED  MINERALS. 

The  general  and  detailed  mineralogy  of  the  tungsten  area  is 
now  better  known  than  it  was  when  the  Report  was  first  issued. 
Though  probably  only  one  new  mineral  has  been  discovered,  other 
associations  are  better  understood.  The  presence  of  a secondary 
feldspar , supposed  to  be  adularia,  had  been  observed  in  a number 
of  veins  in  the  Nederland  and  Beaver  Creek  areas.  Hess  finds 
that  it  is  adularia.  Calcite  had  been  observed  in  the  Conger,  Bed- 
dig,  Townlot  and  other  mines  of  that  vicinity,  but  it  is  not  men- 
tioned in  describing  the  veins.  Fluorite  had  not  been  definitely 
determined,  but  its  presence  was  suspected,  (p.  75).  Within  the 
last  year  two  or  three  specimens  of  ore  carrying  considerable 
amounts  of  purple  fluorite  as  a gangue  mineral  have  been  sent  to 
the  Survey  office.  Free  gold  has  been  found  probably  a dozen 
times  during  the  last  year  in  panning  lean  ores  for  tungsten  tests. 

Hamlinite  (?) : Almost  from  the  first  real  mining  of  tung- 
sten in  Boulder  County  the  presence  of  traces  of  phosphorus  had 
been  noted  in  the  complete  analyses  of  the  ores.  The  writer  thought 
it  might  come  from  apatite  in  the  country  rock  gangue,  since 
apatite  is  commonly  present  in  granite.  But  the  work  of  Hess  and 
Schaller  has  shown  that  there  is  present  in  some  of  the  ores,  a very 
light  green  mineral  having  a specific  gravity  between  2.8  and  3.0, 
and  a perfect  basal  cleavage.  It  appears  to  be  related  to  hamlinite 
but  not  identical  with  it.  On  account  of  its  low  specific  gravity  a 
large  part  of  it  should  disappear  in  concentration,  and  as  a con- 
sequence the  concentrates  should  carry  a lower  ratio  of  phos- 
phorus than  the  raw  ore. 

CONCENTRATION. 

In  the  matter  of  concentration,  the  principal  changes  that  have 
been  adopted  since  the  writing  of  the  report  are  intended  to  avoid 
excessive  sliming  and  to  effect  a readier  saving  of  the  ore.  They 
consist  mainly  in  the  decreased  use  of  stamps,  an  increased  use 


■J  00  MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 

of  rolls,  the  introduction  of  jigs,  and  more  frequent  sizing  and 
classification. 

Experiments  in  the  dry  concentration  of  the  ores  have  given 
some  very  satisfactory  results,  and  it  is  reported  that  at  least  one 
of  the  proposed  new  mills  will  be  equipped  with  these  machines. 

Flotation  has  not,  so  far,  proved  a success  in  the  concentration 
of  tungsten  ores. 

METALLURGY. 

Perhaps  the  most  important  advance  in  the  metallurgy  of 
tungsten  is  the  preparation  of  pure,  ductile,  metallic  tungsten. 
Other  investigations  have  resulted  in  the  modification  and  im- 
provement of  processes  already  in  use.  Some  of  these  have  to  do 
with  the  preparation  of  low  phosphorus  metallic  tungsten  and 
ferro-tungsten  from  phosphorus  bearing  ores.  Others  aim  at  the 
elimination  of  carbon  from  metallic  tungsten  and  the  ferro  alloys. 
Still  others  have  been  directed  to  the  more  satisfactory  handling 
of  high-manganese  tungsten  ores  such  as  hubnerite.  The  recovery 
of  metallic  tungsten  from  steel  scrap  is  another  line  of  investi- 
gation. » 

By  the  Becket  process,  low-phosphorus  ores,  ground  to  100- 
mesh,  are  mixed  with  sulphuric  acid  which  dissolves  out  a large 
proportion  of  the  phosphorus  without  important  loss  of  tungsten. 
High-phosphorus  ores  are  roasted  before  treatment  with  the  acid. 
After  the  acid  treatment  the  ores  are  washed,  dried  and  smelted 
in  the  usual  way. 

The  Goldschmidt  process  has  been  modified  and  adapted  to 
the  direct  treatment  of  ores  and  concentrates. 

Ductile  tungsten  is  prepared  somewhat  as  follows : The  tung- 
sten trioxide,  WO,,  is  purified  by  reducing  it  to  the  dioxide,  W02, 
volatilizing  this  to  the  oxychloride  and  treating  the  product  with 
hydrochloric  acid.  In  volatilizing  the  dioxide,  silica  and  phos- 
phoric acid  are  left  behind  as  a residue.  In  the  acid  treatment 
tungsten  trioxide  is  precipitated  and  arsenic  and  antimony  are 
held  in  solution.  The  trioxide  is  reduced  in  a current  of  hydrogen 
at  a temperature  of  1250°  C.,  and  a fairly  coarse,  pure  metallic 
powder  is  obtained.  The  powder  is  formed  into  rods  by  subjecting 
it  to  enormous  pressure.  The  rods  are  hardened  by  heating  in  an 
atmosphere  of  hydrogen  to  1300°  C.,  and  then  sintered  into  a con- 
nected mass  in  a special  furnace  at  a temperature  of  about  2650°  C. 
The  metal  is  still  brittle,  but  is  rendered  ductile  by  repeated  heat- 
ing and  swaging.  The  ductility  of  pure  tungsten,  so  produced,  is 
very  high.  (See  Min.  Ind.  1912,  pp.  84-89.) 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


101 


USES  OF  TUNGSTEN. 

The  manufacture  of  tungsten  steel  consumes  by  far  the 
largest  part  of  the  tungsten  produced.  Simple  tungsten  steel  is 
an  ordinary  carbon  steel  to  which  tungsten  has  been  added  in  per- 
centages varying  with  the  use  to  which  it  is  to  be  put.  One  of  the 
principal  uses  of  simple  tungsten  steel  is  in  the  manufacture  of 
permanent  magnets  such  as  are  used  in  electric  meters,  the  mag- 
netos of  telephones,  automobile  ignition  systems,  separately  ex- 
cited dynamos,  and  in  certain  scientific  apparatus.  It  is  also  used 
as  a tool  steel  for  finishing  purposes  where  a comparatively  light 
cut  is  required  and  where  high  speed  is  not  important.  It  is  not 
self  tempering,  but  must  be  hardened  by  quenching  in  water  and 
drawing.  A comparatively  new  use  is  for  automobile  valve  stems. 
It  is  estimated  that  the  manufacture  of  permanent  magnets  re- 
quires about  6000  tons  of  simple  tungsten  steel  annually. 

Most  high-speed  steels  contain  two  or  more  alloying  metals. 
Those  containing  two  alloying  metals  are  known  as  quaternary 
steels,  while  those  containing  three  or  more  alloying  metals  are 
called  complex  steels.  The  principal  alloying  metals  used  in  high- 
speed steels  are  tungsten  and  chromium,  but  vanadium,  cobalt  and 
manganese  are  sometimes  used.  Tungsten  is  used  in  both  quater- 
nary and  complex  steels.  The  tungsten  content  generally  ranges 
between  16  and  20  per  cent  and  the  chromium  from  a little  below 
3 to  a little  above  5 per  cent. 

The  use  of  high-speed  steels  effects  great  savings  in  time, 
power  and  overhead  charges  in  the  working  of  metals.  These 
steels  excel  the  old  carbon  tool  steels  in  the  Thickness  of  the  chip 
or  cut,  in  the  rate  of  cutting  and  in  length  of  service  without 
dressing.  They  are  also  used  on  steels  which  are  too  hard  for  the 
carbon  steel  tool. 

The  specification  of  the  U.  S.  government  for  high  speed  tool 
steel  to  be  used  in  the  navy  yards  may  be  taken  as  representing 
very  fairly  the  present  requirements.  These  are  as  follows: 
carbon,  0.55  to  0.75  per  cent.;  chromium,  2.5  to  5.0;  manganese, 
0.05  to  0.03 ; phosphorus,  0.15 ; silicon,  0.3 ; sulphur,  0.02 ; tungsten, 
16.00  to  20.00 ; vanadium,  0.35  to  1.50 ; iron,  72  to  80.5  per  cent. 

TUNGSTEN  STEEL. 

For  several  years  prior  to  1915  the  American  production  of 
tungsten  tool-steel  ranged  from  6000  to  7000  tons.  The  1915  out- 
put far  exceeded  this  figure,  and  that  of  1916  will  be,  in  all  proba- 
bility, double  the  average  of  preceding  years.  A few  years  ago 
there  was  but  little  tendency  toward  uniformity  in  the  composition 


102 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


of  high-speed  steels,  but  experience  has  shown  rather  clearly  the 
most  satisfactory  limits  for  the  various  alloying  metals  with  iron. 

There  is  much  difference  of  opinion  as  to  whether  tungsten 
steel  is  used  in  the  make-up  of  heavy  guns,  mortars  and  howitzers. 
Men  who  should  be  in  a position  to  know  assert  positively  that  it 
is  not  so  used,  while  others  equally  close  to  the  sources  of  informa- 
tion are  quite  as  confident  that  it  is  so  used.  Hibbard  states  that 
the  Austrian  government  uses  tungsten  steel  for  the  tubes  of 
cannon.  It  is  commonly  reported  that  the  French  have  used  tung- 
sten steel  even  more  extensively  in  artillery,  and  that  the  British 
arsenals  are  using  it  in  the  bodies  of  field  guns.  Fink,  who  is 
unusually  well  posted  in  the  technology  of  tungsten,  says  in  a 
private  communication  dated  March  16,  1916:  “Tungsten  steel 
enters  into  the  composition  of  our  large  guns  and  also  smaller 
ammunition.”  It  is  used  in  the  machining  of  shrapnel,  but  not 
in  the  composition. 

As  to  its  use  in  armor  plate  there  is  equal  difference  of 
opinion.  One  buyer  who  has  acted  as  agent  for  the  U.  S.  govern- 
ment on  different  occasions  states  positively  that  the  U.  S.  Navy 
specifications  for  armor  plate  and  those  of  certain  other  govern- 
ments include  a certain  percentage  of  tungsten.  It  is  objected 
that  tungsten  makes  steel  harder,  but  more  brittle,  and,  therefore, 
less  suited  to  the  manufacture  of  armor  plate.  This  is  true  up  to 
a certain  percentage  of  tungsten,  but  Gledhill  has  shown  that 
steel  with  18  to  27  per  cent  of  tungsten  is  tough  and  not  brittle. 
In  the  first  issue  of  this  Report  attention  was  called  to  the  varying 
effects  of  tungsten  on  steels.  The  use  of  high-speed  steel  has 
brought  out  similar  facts  in  relation  to  the  speed  of  highest  effici- 
ency in  cutting. 

Wrought  tungsten,  on  account  of  its  high  specific  gravity,  is 
being  tested  as  a metal  for  rifle  bullets  and  other  small  projectiles. 
It  is  highly  probable  that  the  equipment  of  factories  with  high- 
speed  tool  steel,  for  manufacturing  munitions  of  war  is  respon- 
sible for  a very  large  part  of  the  extraordinary  demand  for  the 
metal. 

METALLIC  TUNGSTEN. 

Ductile,  metallic  tungsten  has  become  a market  commodity 
within  the  last  three  or  four  years.  This  has  greatly  extended  the 
minor  uses  of  tungsten,  and  researches  now  under  way  promise 
many  interesting  discoveries  and  new  uses  for  this  magic  metal. 
Its  physical  and  chemical  properties  are  of  such  an  extraordinary 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  103 

character  that  it  is  safe  to  predict  a remarkably  wide  field  of  use- 
fulness in  the  arts  and  sciences. 

A few  of  the  possibilities  of  ductile  tungsten  are  here  listed 
from  a paper  by  Dr.  C.  G.  Fink  of  the  General  Electric  Company’s 
research  staff. 

1.  A substitute  for  platinum  and  platinum  alloys  as  contact 
points  in  spark  coils,  voltage  regulators,  telegraph  relays,  resisters 
in  electrical  laboratory  furnaces,  and  as  targets  in  Roentgen  tubes. 

2.  In  the  form  of  gauze  it  could  be  used  for  the  separation  of 
solids  from  acid  liquors,  as,  for  example  the  removal  of  sludge 
from  copper  refining  baths ; the  manufacture  of  acid  proof  dishes 
and  tubes. 

3.  In  calibrating  instruments  and  apparatus,  such  as  stand- 
ard weights,  standard  resistances,  electrical  meters,  and  many 
others. 

4.  Its  chemical  stability  and  resistance  to  change  under 
atmospheric  conditions  make  it  suitable  for  many  uses  where 
delicate,  yet  strong  metallic  wires,  points  and  springs  are  needed, 
as  in  watch  springs,  pen  points,  drawing  dies,  cross  hairs  in  tele- 
scopes and  other  optical  instruments,  galvanometer  suspensions 
and  the  wires  of  musical  instruments. 

The  ductile  metal  is  now  drawn  through  dies  into  wire  of 
any  desired  size  down  to  a diameter  of  0.0002  inch,  (one-sixth  the 
diameter  of  a fine  human  hair).  (The  dies  for  the  finest  wire 
consist  of  drilled  diamonds.)  As  a consequence,  the  metallic  tung- 
sten wire  filament  for  incandescent  lamps  has  completely  replaced 
the  “paste”  filaments  described  in  the  first  issue  of  this  Report,  and 
the  carbon  filament  is  doomed.  In  1913  the  gas-filled  incandescent 
tungsten  lamp  was  placed  on  the  market.  This  consists  of  a 
metallic,  tungsten  filament  in  a globe  filled  with  nitrogen.  This 
change  reduces  the  consumption  of  current  to  about  one-half  watt 
per  candle  power,  as  compared  with  1.25  watts  per  candle  power 
for  the  vacuum  lamp.  The  life  of  the  filament  is  also  prolonged 
because  of  the  reduced  rate  of  evaporation  of  the  metallic  tung- 
sten in  an  atmosphere  of  nitrogen. 

The  light  produced  by  the  gas-filled  lamp  approaches  day-light 
in  whiteness. 

It  is  estimated  that  the  total  American  consumption  of  metal- 
lic tungsten  for  lamp  filaments  does  not  exceed  two  tons  per  year. 

THE  PHYSICAL  AND  CHEMICAL  PROPERTIES  OF  THE  METAL. 

Specific  gravity,  19.3  to  20.2. 

Tensile  strength  in  pounds  per  sq.  inch,  610,000. 


104 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


(Tensile  strength  of  extra  steel,  450,000). 

Modulus  of  elasticity  in  pounds  per  square  inch  60,000,000. 

(Steel  30,000,000). 

Melting  point,  3267°  C.,  (This  is  much  higher  than  that  of  any 
other  metal,  and  probably  higher  than  that  of  any  known  sub- 
stances except  carbon,  and  perhaps,  boron.  Platinum  melts  at 
1710°  C.). 

Hardness,  variable,  ranging  from  4.5  to  8,  depending  upon 
treatment.  The  hardest  will  easily  scratch  glass. 

Coefficient  of  expansion  at  18°  C.  is  0.0000035  while  that  of 
platinum  is  0.0000088. 

It  is  practically  non-magnetic. 

It  is  insoluble  in  hydrochloric,  nitric,  sulphuric  and  hydro- 
fluoric acids,  sodium  and  potassium  hydroxides  and  mixtures  of 
potassium  chromate  and  sulphuric  acid.  It  is  soluble  in  mixtures 
of  hydrofluoric  and  nitric  acids  and  in  fused  nitrates  and 
peroxides. 

ALLOYS. 

Many  new  alloys  have  been  patented,  and  some  of  these  have 
been  placed  on  the  market  for  various  purposes.  An  alloy  con- 
taining 20  to  60  per  cent  tungsten  and  80  to  40  per  cent  platinum 
is  recommended  for  electrical  contacts  and  for  jewelry.  Alloys  of 
tungsten  and  thorium  have  been  patented.  The  tensile  strength 
of  aluminum  is  increased  by  the  addition  of  about  1 per  cent  of 
tungsten.  Duralium  is  an  alloy  of  tungsten  and  aluminum  con- 
taining 2 to  3 per  cent  of  tungsten.  A new  type  metal  contains: 
tungsten  10  parts,  copper  10  parts  and  aluminum  80  parts. 

Stellite , an  alloy  of  cobalt  and  chromium,  invented  by  Haynes, 
has  been  modified  and  greatly  improved  for  certain  purposes  by 
the  addition  of  tungsten.  When  the  chromium  is  held  at  15  per 
cent  and  tungsten  added  in  amounts  varying  from  5 per  cent  to 
40  per  cent,  the  hardness  and  cutting  qualities  of  tools  formed 
from  it  are  greatly  increased.  Tests  indicate  that  it  far  surpasses 
the  high-speed  steels.  (Alloys  of  Cobalt  with  Chromium  and 
Other  Metals  by  Elwood  Haynes,  Bull.  A.  I.  M.  E.,  Feb.  1913,  pp. 
249-255. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  105 


TUNGSTEN  PRODUCTION  ON  BASIS  OF  60  % WO*. 


Weight  Tons 

Range  per  unit 

Value 

1907 

1,146 

$5.00-$9.00 

$573,643 

1908 

587 

Very  Poor  Market 

164,220 

1909 

993 

$5.00-$9.0o 

391,160 

1910 

1,221 

$6.50-$8.50 

553,100 

1911 

730 

$4.50-$8.50 

261,492 

1912 

775 

$5.60-$7.50 

293,611 

1913 

953 

Rather  Steady  at  about  $7.50 

428,726 

1914 

630 

$5.85-$9.00 

252,000 

1915 



$5.50-$45.00 

106 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


BIBLIOGRAPHY. 

ABBREVIATIONS. 

A.  I.  M.  E. — Transactions  of  the  American  Institute  of  Mining 
Engineers. 

Am.  Chem.  Jou. — American  Chemical  Journal. 

Am.  Jou.  Sci. — American  Journal  of  Science. 

Ec.  Geol. — Economic  Geology. 

E.  M.  J. — Engineering  and  Mining  Journal. 

Eng.  Mag. — Engineering  Magazine. 

J.  A.  C.  S. — Journal  of  American  Chemical  Society. 

Jou.  I.  and  S.  I.— Journal  of  the  Iron  and  Steel  Institute. 

J.  S.  C.  I. — Journal  of  the  Society  of  Chemical  Industry. 

Min.  and  Geol.  Mus. — Mineral  and  Geological  Museum. 

Min.  Ind. — Mineral  Industry. 

Min.  Jou. — Mining  Journal. 

M.  R. — Mineral  Resources. 

Min.  Rep. — Mining  Reporter. 

Min.  Sci.  Press — Mining  and  Scientific  Press. 

Quar.  Jou.  Geol.  Soc. — Quarterly  Journal  of  Geological  Society. 

Soc.  of  Engs,  and  Mets. — Society  of  Engineers  and  Metallurgists. 

AUTHORS  AND  TITLES. 

1.  Allen  (E.  T.)  and  Gottschalk  (V.  H.).  Tungsten,  Research  on  the 

Oxides  of.  Am.  Chem.  Jou.,  27,  pp.  328-40. 

2.  Annabl  (H.  W.).  “Tungsten  Ores,”  Assay  of.  E.  M.  J.,  72,  p.  63, 

3.  Atkin  (A.  J.  R.).  Scheelite,  “Genesis  of  Gold  Deposits  of 

Barkerville,  B.  C.,  and  Vicinity.”  London  Quar.  Jou.  Geol.  Soc., 
60,  pp.  389-93. 

4.  Aubury  (L.  E.).  Tungsten.  Bull.  38,  California  State  Mining 

Bureau,  p.  372. 

5.  Auchy  (Geo.).  “Tungsten  in  Steel,  Rapid  Determination  of.”  J. 

A.  C.  S.,  21,  pp.  239-245. 

6.  Auerbach  (H.  S.).  “Tungsten-ore  Deposits  of  the  Coeur  d’Alene, 

Idaho.”  E.  M.  J.,  86,  pp.  1146-48. 

7.  Baskerville  (C.).  “Tungsten.”  E.  M.  J.,  87,  p.  203. 

8.  Berg  (C.).  “Tungsten  in  Aluminum  Alloys.”  German  Patent 

No.  123,820. 

9.  BWlher  (P.,.  “w03-  Tungstic  Oxide,  Use  of,  in  Producing  Coloi 

Resists  and  Discharges.”  J.  S.  C.  I.,  19,  p.  1107. 

10.  Blair  (T.).  “Tungsten  Alloys.”  Sheffield  Soc.  of  Engs,  and  Mets., 

Dec.,  1894. 

11.  Blake  (W.  P.).  Hubnerite  as  an  Addition  to  Steel,  “Hubnerite 

in  Arizona.”  A.  I.  M.  E.,  28,  p.  546. 

12.  Blake  (W.  P.).  Wolframite  from  Cornwall,  England,  “Hub- 

nerite in  Arizona.”  A.  I.  M.  E.,  28,  p.  546. 

13.  . “Tungsten.”  Min.  Ind.,  16,  pp.  888-90. 

14.  . Hubnerite  in  Mammoth  District,  Nevada,  “Hub- 

nerite in  Arizona.”  A.  I.  M.  E.,  28,  p.  543. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


107 


15.  . “Wolframite  in  Arizona.”  Min.  Ind.,  7,  pp.  719-22. 

16.  . Wolframite  (manganiferous),  in  Arizona,  “Hub- 

nerite  in  Arizona.”  A.  I.  M.  E.,  28,  p.  543. 

17.  Borchers  (W.).  “Notes  on  the  Metallurgy  of  Tungsten.”  Min. 

Ind.,  8,  p.  632. 

18.  Bodenbender  (G.).  “Wolframite  in  Quartz  Veins  in  Granite.” 

Zeitschr.  fur  Prakt.  Geol.,  1894.  p.  409. 

19.  Boggeld  (O.  B.).  Mineralogia  Groenlandica,  Contr.  to  Min.  No. 

6,  Min.  and  Geol.  Mus.  of  Univ.  of  Copenhagen. 

10.  Bullnheimer  (F.).  “Determination  of  Tungsten  in  Ores.”  J.  S. 
C.  I.,  19,  p.  1147. 

21.  Carpenter  (F.  R.)  and  Headden  (W.  P.).  Wolframite  in  Black 

Hills.  “Influence  of  Columbite  Upon  Tin-Assay.”  A.  I.  M.  E.,  17, 
p.  786. 

22.  Church  (J.  A.).  Wolframite  in  Arizona,  “The  Tombstone, 

Arizona,  Mining  District.”  A.  I.  M.  E.,  33,  p.  3. 

23.  Collins  (J.  H.).  Tungsten  in  Cornwall,  England,  “Notes  on 

Some  of  the  Less  Common  Metals  of  the  West  of  England.”  E. 
M.  J.,  81,  p..  1225. 

24.  Conder  (H.).  “Wolframite  and  Tungsten.”  Min.  Jou.,  London, 

Aug.  12,  1905,  copied  in  Queensland  Govt.  Min.  Jou.,  Oct.  14, 
1905. 

25.  Cooper  (C.  A.).  “Tungsten  Ores  of  San  Juan  County,  Colo- 

rado.” E.  M.  J.,  67,  p.  499. 

26.  Cross  (W.)  and  Hillebrand  (W.  F.).  “Mineralogy  of  the  Rocky 

Mountains.”  U.  S.  G.  S.,  Bull.  20,  pp.  90-96. 

27.  Day  (D.  T.).  “Tungsten.”  M.  R.,  1883,  pp.  431-33. 

28.  ’.  “Tungsten  Steel.”  M.  R.,  1886,  p.  218. 

29.  . “Tungsten,”  Statistics  of.  M.  R.,  1883-4,  pp.  574-5. 

30.  Delepine  (M.).  “Preparation  of  Pure  Tungsten.”  J.  S.  C.  I., 

19,  p.  829. 

31.  “Reduction  of  Tungsten  Anhydride  for  Preparation 

of  Pure  Tungsten.”  J.  S.  C.  I.,  19,  p.  908. 

32.  Dunsten  (B.).  “Wolfram,  How  to  Know  It.”  Min.  Rep.,  Dec. 

1,  1904,  p.  580. 

in  Queensland  Gover’t.  Min.  Jou.,  July  15,  1905). 

Report,  Geol.  Survey,  Queensland,  1904  (Digest  of  same  article 
in  Queensland  Gover’t  Min.  Jou.,  July  15,  1905). 

34.  Dana.  Wolframite,  Hubnerite,  Ferberite,  Scheelite,  etc.  “Sys- 

tem o£  Mineralogy,”  pp.  981-992;  Also 
Wolframite,  Raspite,  etc.  “First  Appendix  to  System  of  Mineralogy,” 
p.  73,  p.  58. 

35.  Fermor  (L.  L.).  “Wolfram  in  Nagpur  District,  India.”  Rec. 

Geol.  Sur.  of  India,  36,  Pt.  IV.,  p.  11. 

36.  Fritchie  (O.  P.).  “Determination  of  Tungsten  in  Ores.”  J.  S. 

C.  I.,  20,  p.  840. 

37.  Granger  (A.).  Tungsten  in  Pottery  Glazes.  Com.  Rend.,  140, 

pp.  935-6;  (Abstract  in  J.  S.  C.  I.,  24,  p.  498). 


108 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


38.  . “Tungsten  Glazes  for  Porcelain.”  Com.  Rend.,  2, 

p.  106,  1898;  Digest  in  E.  M.  J.,  67,  p.  292. 

3 9.  Garrison  (L.  F. ).  Alloys  of  Aluminum  with  Tungsten,  Titanium 
and  Manganese,  “Greene-Wahl  Process,  Etc.”  A.  I.  M.  E.,  21, 
p.  896. 

40.  . Tungsten  Alloys,  Uses,  Character,  “Tungsten  and 

Steel.”  U.  S.  G.  S.,  16th  Ann.  Rep.,  Pt.  Ill,  pp.  615-23. 

41.  Genth  (F.  A.).  Wolframite  and  Scheelite,  from  North  Carolina, 

Analyses  of.  U.  S.  G.  S.  Bull.  74,  p.  80. 

42.  Gledhill  (J.  M.).  “Development  and  Use  of  High-Speed  Tool- 

Steel.”  Bi-monthly  Bull.,  A.  I.  M.  E.,  Mar.,  1905,  p.  337;  (Also 
in  Jou.  I.  and  S.  I.,  Oct.,  1904). 

43.  Goodale  (C.  W.)  and  Akers  (W.  A.).  Hubnerite,  Presence  of 

in  Silver  Ores,  “Concentration  Before  Amalgamation  for  Low- 
Grade  Partially  Decomposed  Silver  Ores.”  A.  I.  M.  E.,  18,  p.  248. 

44.  ■.  “Porcelain  Furnace  for  Production  of  Blue  Glaze.” 

J.  S.  C.  I.,  17,  p.  925. 

45.  Greenawalt  (W.  E.).  “Tungsten  Deposits  of  Boulder  County, 

Colorado.”  E.  M.  J.,  83,  pp.  951-2. 

46.  Guetat  and  Chavanne.  “Manufacturing  of  Tungsten  Alloys  and 

Iron  Alloys.”  J.  S.  C.  I.,  1,  p.  152. 

47.  Gurlt  (A.).  “Remarkable  Deposit  of  Wolfram-ore  in  the  United 

States.”  A.  I.  M.  E.,  22,  pp.  236-242. 

48.  . “Etymology  of  Name  ‘Wolframite.’  ” Id.,  p.  237. 

49.  — . Early  Manufacture  of  Wolfram-steel  in  Austria.  Id., 

p.  237. 

50.  Guillet  (L.).  “Alloy  Steels.”  Eng.  Mag.,  Dec.,  1904,  p.  443. 

51.  Hadfield  (R.  A.).  “Alloys  of  Iron  and  Tungsten.”  Jou.  I.  and 

S.  I.,  1903,  Pt.  II.,  p.  28,  et  seq. 

52.  Handy  (J.  O.).  “Analysis  of  Tungsten-Aluminum  Alloys.”  J.  A. 

C.  S.,  18,  p.  774. 

53.  Hallopeau  (L.  A.).  “Production  of  Crystallized  Tungsten  by 

Electrolysis.”  J.  S.  C.  I.,  18,  p.  50. 

54.  Helmliacker  (R.).  “Tungsten.”  J.  S.  C.  I.,  15,  p.  656. 

55.  . “Relative  Resistance  of  Tungsten  and  Molybdenum 

Steel.”  E.  M.  J.,  66,  p.  430. 

5 6.  Hess  (F.  L.).  “Nickel,  Cobalt,  Tungsten,  Vanadium,  etc.”  M. 

R. ,  U.  S.  G.  S.,  1906,  pp.  519-40. 

57.  — : . “Tungsten,  Nickel,  Cobalt,  etc.”  M.  R.,  Pt.  I.,  U. 

S.  G.  S.,  1907,  pp.  711-17. 

58.  Hillebrand  (W.  F.).  “Hubnerite,”  Description  and  Analysis  of, 

from  Ouray  County,  Colo.,  and  from  near  Phillipsburg,  Mont. 
Bull.  U.  S.  G.  S.,  20,  p.  96. 

59.  Hobbs  (Wm.  H.).  Scheelite,  “The  Old  Tungsten  Mine  at 

Trumbull,  Connecticut.”  U.  S.  G.  S.,  22nd  Ann.  Rep.,  Pt.  II., 
pp.  7-22. 

60.  Howe  (H.  M.).  “The  Metallurgy  of  Steel.”  p.  81. 

61.  . “Iron,  Steel  and  Other  Alloys.”  1903. 

62.  Hutton  (R.  S.).  “Separation  of  WOs  from  Minerals.”  J.  S.  O. 

I.,  18,  p.  171. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


109 


63.  Electrochemical  Ind.,  5. 

64.  Huznetzow  (A.)  and  Moissan  (H.).  “Chromium-Tungsten- 

Carbide.”  E.  M.  J.,  7 6,  p.  433. 

65.  Irving  (J.  D.).  Wolframite  in  Arizona,  p.  694;  in  Colorado,  p. 

694;  in  Idaho,  p.  694;  in  Nevada,  p.  693;  in  Black  Hills,  South 
Dakota,  p.  683;  Wolframite,  Analysis  of,  p.  691;  Tungsten  Min- 
erals, Source  of,  p.  694;  Wolframite  in  Cornwall,  England,  p. 
694.  All  come  under  discussion  of  “Some  Recently  Exploited 
Deposits  of  Wolframite  in  the  Black  Hills  of  South  Dakota.”  A. 
I.  M.  E.,  31,  pp.  683-695. 

66.  . “Tungsten  Ores  in  the  Black  Hills,  South  Dakota.” 

Professional  Paper  26,  pp.  158,  163-69. 

67.  Johnston  (R.  A.  A.).  “Tungsten  and  Molybdenum.”  M.  R.  of 

Canada,  1904. 

68.  Joseph  (M.  H.).  “Tungsten  Ores  in  Washington.”  E.  M.  J., 

81,  p.  409. 

69.  Kellog  (L.  O.).  “Wolframite  Ores  of  Cochise  Mining  District.” 

Ec.  Geol.,  I.,  p.  654. 

70.  Lee  (H.  A.).  “Tungsten  Ores.”  Colo.  Bureau  Mines,  Bull.  4, 

p.  12,  1901;  (Also  5,  p.  20,  1902). 

71.  Lindgren  (W.).  Scheelite  in  Virtue  District,  “Gold  Belt  of  Blue 

Mountains  of  Oregon.”  22nd  Ann.  Rep.,  U.  S.  G.  S.,  Pt.  II.,  p. 
644. 

72.  . Wolframite,  “Relation  of  Ore-Deposition  to  Physical 

Conditions.”  Ec.  Geol.,  2,  pp.  453-463. 

73.  . “Some  Gold  and  Tungsten  Deposits  of  Boulder 

County,  Colorado.”  Ec.  Geol.,  2,  pp.  111-112. 

74.  Martino.  “Manufacture  of  Tungsten-Alloys.”  J.  S.  C.  I.f  3,  p. 

180. 

75.  McKenna  (A.  G.).  “Analysis  of  Chrome  and  Tungsten  Steels.” 

E.  M.  J.,  70,  p.  124. 

76.  Meeks  (R.).  “Tungsten.”  Min.  Ind.,  14,  pp.  557-61;  Also  Min. 

Ind.,  1906,  pp.  744-47. 

77.  Merrill  (G.  P.).  Wolframite,  “Non-Metallic  Minerals,  Their 

Occurrence  and  Uses.”  Jno.  Wiley  & Sons. 

78.  Metcalf  (W.).  Tungsten,  Effect  on  Steel  Rails,  “Discussion  of 

Dr.  Charles  B.  Dudley’s  Papers  on  Steel  Rails.”  A.  I.  M.  E.,  7, 
p.  380. 

79.  Moissan  (H.).  “Researches  on  Tungsten.”  J.  S.  C.  I.,  15,  p.  598. 

80.  Moses  (A.  J.).  “Crystallization  of  Luzonite,  and  Other 

Crystallographic  Studies.”  Am.  Jou.  Sci.,  4th  Series,  20,  pp. 
277-284,  1905. 

81.  Nason  (H.  B.).  “Wolframite  and  Scheelite.”  Wohler’s  Min. 

Analysis. 

82.  O’Hara  (C.  C.).  “Mineral  Wealth  of  the  Black  Hills.”  S.  D. 

Geol.  Sur.  Bull.  No.  S,  pp.  68-72;  and  S.  D.  School  of  Mines 
Bull.  No.  6,  pp.  71-75,  1902. 

83.  Osmond.  “Influence  of  Tungsten  on  Iron  and  Steel.”  J.  S.  C. 

I.,  9,  p.  866, 


110 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


84.  Pearce  (R.).  Hubnerite  in  Copper  Veins,  Butte,  Mont.,  “Asso- 

ciation of  Minerals  in  tbe  Gagnon  Vein,  Butte  City,  Montana." 
A.  I.  M.  E.,  16,  p.  64. 

85.  Plummer  (J.).  “Australian  Tungsten."  Mining  World,  Dec.  3, 

1904. 

8 6 Pratt  (J.  H.  ).  “Tungsten,  Molybdenum,  Uranium  and  Vana- 
dium.” 21st  Ann.  Rep.,  Pt.  VI.,  pp.  299-305. 

87.  , M.  R.,  1901,  pp.  261-268. 

88.  . M.  R.,  1900,  pp.  257-265. 

89.  . M.  R.,  1902,  pp.  285-288. 

90.  . M.  R.,  1903,  pp.  285-310. 

91  . m.  R.,  1904,  pp.  326-338. 

92.  . M.  R.,  1905,  pp.  410-412. 

93.  Phillip  (J.).  “Tungsten  Bronzes."  J.  A.  C.  S.,  4,  p.  266. 

94.  Preusser  (J.).  “Determination  of  Tungsten  in  Tungsten  Alloys." 

J.  A.  C.  S.,  11,  p.  53. 

95.  Ransome  (F.  L.).  Hubnerite.  U.  S.  G.  S.  Geol.  Atlas,  Silverton 

Folio,  120,  p.  7. 

96.  — . Tungsten  Ores1  (Hubnerite)  in  Silverton  Region. 

U.  S.  G.  S.,  Bull.  182,  pp.  86-7,  256. 

97.  Rickard  (F.).  “Notes  on  Tungsten  Deposits  in  Arizona."  E.  M. 

J.,  78,  p.  263. 

98.  Roscoe  and  . Schorlemmer.  “Treatise  on  Chemistry."  2,  pp. 

1057-78. 

99.  Rossi  (A.  J.).  Progress  in  the  Manufacture  and  use  of  Titanium 

and  Similar  Alloys.  Min.  Ind.,  11,  pp.  693-6. 

100.  Rothwell  (R.  P.).  and  Borchers  (W.).  “Tungsten."  Min.  Ind., 

8,  p.  657. 

101.  Rowe  (J.  P.).  “Tungsten  in  Coeur  d’Alene  Mining  District, 

Idaho."  Mining  World,  29,  p.  77  8. 

102.  Schneider.  “Manufacture  of  Tungsten  Alloys  and  Iron  Alloys." 

J.  S.  C.  I.,  4,  p.  676. 

103.  Simmons  (Jesse).  “Tungsten  Ores  in  Black  Hills."  Min.  Rep., 

50,  pp.  217-18. 

104.  Simonds  (F.  W.).  Wolframite,  “The  Minerals  and  Mineral 

Localities  of  Texas."  Sci.,  New  Series,  14,  p.  796. 

105.  Skewes  (E.).  “Magnetic  Separation  of  Tungsten  and  Tin."  T. 

S.  C.  I.,  22,  p.  1132. 

106.  Smith  (E.  F.)  and  Bradbury.  “Estimation  of  Tungstic  Acid." 

J.  S.  C.  I.,  10,  p.  1037. 

107.  Smith  (F.  D.).  “Os*ceola,  Nevada,  Tungsten  Deposits."  E.  M. 

J.,  73,  pp.  304-5. 

108.  Spurr  (J.  E.).  Tungsten  in  Siliceous  Rocks,  “Igneous  Rocks 

and  Their  Segregation  or  Differentiation  as  Related  to  Occur- 
rence of  Ores."  A.  I.  M.  E.,  33,  p.  322. 

109.  Stansfield  (A.).  Ferro-Alloys,  “The  Electric  Furnace,  Its 

Evolution,  Theory  and  Practice."  pp.  136-42. 

110.  Stavenhagen  (A.).  “Preparation  of  Tungsten."  J.  S.  C.  I.,  19, 

p.  52. 

lUf  — “Metallic  Tungsten."  J.  S.  C.  I.,  18,  p.  687. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Ill 


112.  Sternberg  and  Beutsch.  “Production  of  Tungsten.”  J.  S.  C.  I., 

12,  p.  845. 

113.  Thomas  (K.).  Boulder  County  Tungsten  District.  Min.  World, 

Vol.  23. 

114.  Turner  (T.).  Aluminum  Process  for  Ferro-Alloys,  “Iron,  the 

Metallurgy  of.”  p.  271;  (Also  in  Cassiars’  Magazine,  1905,  p. 
360). 

115.  Thyng  (W.  S.).  “Tungsten  Deposits  in  Washington.”  E.  M.  J.,  73, 

p.  418. 

116.  Uppenborn  (F.).  Tungsten  Filaments.  J.  S.  C.  I.,  25,  p.  876. 

117.  Van  Wagenen  (H.  R.).  “Tungsten  in  Colorado.”  Bull.  Colo.  Sell. 

Mines,  3,  p.  138. 

118.  Walker  (E.).  Tin  Ore  Dressing,  East  Pool,  Cornwall.  E.  M.  J., 

83,  pp.  941,  1092. 

119.  Walker  (T.  L. ).  “A  Review  of  the  Minerals  of  Tungsten  and  Mey- 

macite.”  Am.  Jou.  Sci.,  175,  p.  305. 

120.  . “The  Occurrence  of  Tungsten  Ores  in  Canada.”  Trans. 

Can.  Min.  Inst.,  11,  p.  193. 

121.  Weeks  (F.  B.).  “An  Occurrence  of  Tungsten-ores  in  Eastern 

Nevada.”  21st  Ann.  Rep.  U.  S.  G.  S.,  Pt.  VI.,  pp.  319-20; 
(Abstract:  E.  M.  J.,  72,  pp.  8-9). 

122.  . Tungsten  Deposits  in  the  Snake  Range,  White  Pine 

County,  Eastern  Nevada.  U.  S.  G.  S.  Bull.  340,  p.  263. 

123.  Ziegler.  “Analysis  of  Tungsten.”  J.  S.  C.  I.,  9,  p.  216. 

ANONYMOUS  NOTES  AND  ARTICLES. 

124.  Alloys  of  Tungsten: 

(a)  “Tungsten  Steel  Manufacture.”  (Patent.)  J.  S.  C.  I.,  24, 

p.  977. 

(b)  Tungsten  Alloys,  “Metallics.”  E.  M.  J.,  82,  p.  1076. 

125.  Deposits,  Mining  and  Production: 

(a)  Tungsten,  Production  of,  “Mineral  Output  of  California.” 

E.  M.  J.,  82,  pp.  876,  892. 

(b)  Tungsten  in  Queensland,  “Notes  from  Eastern  Australia.” 

E.  M.  J.,  81,  p.  849. 

(c)  Tungsten,  Production,  “Queensland  Mineral  Production.” 

E.  M.  J.,  75,  p.  636;  (Also  76,  p.  711). 

(d)  Tungsten  Production  in  Great  Britain.  E.  M.  J.,  77,  p. 

430;  (Also  E.  M.  J.,  78,  p.  334). 

(e)  Tungsten  Ore  in  Brazil.  E.  M.  J.,  81,  p.  747. 

(f)  Tungsten  in  Western  Australia,  “The  Rare  Minerals  of 

Australia.”  E.  M.  J.,  78,  p.  900. 

(g)  Tungsten  in  California,  “Special  Correspondence.”  E.  M. 

J.,  79,  p.  1013. 

(li)  “Scheelite  Mining  in  New  Zealand.”  Queensland  Govt. 
Min.  Jou.,  Feb.,  1906. 

(i)  Wolframite  in  Northern  Part  of  Queensland.  E.  M.  J.,  78, 

p.  724. 

(j)  Wolfram  Mining  in  Spain.  “Revista  Minera,”  Dec.  24, 

1906. 

(k)  Tungsten  in  California.  E,  M,  Jv  83?  p.  1063, 


112 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


(l)  Tungsten,  Nevada.  E.  M.  J.,  84,  p.  1086. 

(m)  Great  Britain.  Min.  World,  26,  p.  477. 

(n)  Production.  Min.  Ind.,  11,  p.  598. 

(o)  Hubnerite  in  Montana.  Min.  Sci.  Press,  96,  p.  265. 

(p)  Production.  Min.  ReR.,  50,  p.  564. 

(q)  Wolframite  Mined  in  “Rhodesia,  Africa.”  E.  M.  J.,  82,  p. 

614. 

(r)  Tungsten  Mining  in  California.  E.  M.  J.,  86,  p.  573. 

(s)  Tungsten,  Production  and  Uses.  E.  M.  J.,  73,  p.  7 60. 

(t)  “Tungsten  in  Russia.”  E.  M.  J.,  65,  p.  581. 

(n)  Tungsten  Ores  Described.  E.  M.  J.,  71,  p.  4 67. 

(v)  Nevada,  Production.  E.  M.  J.,  86,  p.  1228. 

(w)  Round  Mountain,  Nevada.  Min.  Sci.  Press,  94,  p.  799. 

(x)  Hubnerite  in  Montana.  Min.  Sci.  Press,  96,  p.  265. 

(y)  Production.  Min.  Ind.,  9,  p.  657. 

126.  Metallurgy  of  Tungsten: 

(a)  Tungsten  from  Tin,  Removing,  “Metallics.”  E.  M.  J.,  32, 

p.  68. 

(b)  Tungsten,  Preparation  of.  J.  S.  C.  I.,  25,  p.  1099. 

127.  Uses  of  Tungsten: 

(a)  Tungsten,  Use  of,  “Metallics.”  E.  M.  J.,  75,  p.  551. 

(b)  Tungsten,  Use  of,  “Demand  for  Tungsten  Ores'.”  E.  M.  J., 

77,  p.  725. 

(c)  Tungsten,  Use  of  in  Germany,  “Rare  Minerals  of  Australia.” 

E.  M.  J.,  78,  p.  900. 

(d)  “Tungsten:  Its  Use  and  Value.”  E.  M.  J.,  78,  p.  750. 

(e)  “Tungsten.”  Encyclopedia  Britannica. 

(f)  Mordant  and  Color  Resists.  J.  S.  C.  I.,  19,  pp.  740,  1107. 

(g)  Tungsten  and  Tungstates  and  Other  Tungsten  Compounds. 

J.  S.  C.  I.,  19,  p.  542. 

(h)  “Chromium-Tungsten,”  Carbide.  E.  M.  J.,  76,  p.  776. 

(i)  Tungsten  Lamps  in  Michigan.  Min.  Sci.  Press,  96,  p.  265. 

p.  265. 

(j)  Tungsten  Filaments,  Preparation  of.  J.  S.  C.  I.,  25,  p.  116. 

ADDITIONAL  BIBLIOGRAPHY. 

Ackermann  (E.).  “Production  du  Wolfram  au  Colorado.”  Rev.  de  Chim. 
Ind.,  Apr.,  1911. 

Arnold  (J.  O.)  and  Read  (A.  A.).  The  chemical  and  mechanical  relations 
of  iron,  tungsten,  and  carbon,  and  of  iron,  nickel,  and  carbon. 
Proc.  Inst.  Mech.  Eng.,  March-May,  1914,  pp.  223-279. 

Ball  (Lionel  C.,.  “A  Resume  of  Recent  Field  Studies  on  Tungsten  Ore.” 

Queensland  Gover’t.  Jou.,  Jan.  15,  1913. 

Baskerville  (C.).  “The  Rare  Metals-Tungsten.”  E.  M.  J.,  87.  p.  203. 
Brayshau  (Shipley  N.).  “The  Hardening  of  Carbon  and  Low  Tungsten 
Tool  Steels.”  Eng.  Mag.,  Dec.,  1912. 

Carl  (P.  H.).  “Tungsten  and  Vanadium  in  Colorado  and  Elsewhere.”  Mg. 
Sci.,  63,  pp.  92-94. 

Coolidge  (W.  D.).  “Metallic  Tungsten  and  Some  of  its  Applications.” 
Proc.  A.  I.  E.  E.,  June,  1912. 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY.  113 

Dalzell  (T.  J.).  “Tungsten.”  (Review)  Biennial  report  of  the  Colo.  State 
Bur.  of  Mines,  1911,  pp.  21-23. 

“Deep  Mining  for  Tungsten  in  Colorado.”  Mg.  Sci.,  63, 

498-499. 

Dana.  Wolframite,  Hubnerite,  Scheelite,  Raspite.  “Second  Appendix  to 
System  of  Mineralogy.”  pp.  Ill,  53,  91,  87. 

Ekeley  (J.  B.,.  “Colorado  Tungsten.”  Colo  Univ.  Studies,  Vol.  6,  No.  2, 

1909,  pp.  93-96. 

Ekeley  (J.  B.)  and  Kendall  (G.  D.  Jr.).  “A  New  and  Short  Method  for 
the  Determination  of  Tungstic  Acid  in  Tungsten  Ores.”  West. 
Chem.  and  Met.,  Jan.,  1908,  5 pp. 

Edwards  (E.  T.).  Composition  of  High-Speed  Tool  Steel.  Iron  Age,  8 9, 
957-60. 

Fink  (Colin  G.).  “Ductile  Tungsten  and  Molybdenum.”  Chem.  Eng.,  Aug., 

1910,  3|  pp. 

“Ductile  Tungsten.”  Met.  and  Chem.  Eng.,  Sept.  12,  1912. 

i “Applications  of  Ductile  Tungsten.”  Jou.  Ind.  Eng.  Chem., 

Jan.,  1913,  p.  8. 

“Tungsten.”  Min.  Ind.,  22,  pp.  762-71. 

“Tungsten.”  Min.  Ind.,  23,  pp.  745-60. 

Fleck  (Herman).  “Tungsten.”  Colo.  Sch.  of  Mines  Quart.,  Vol.  10,  Oct., 
1915,  pp.  32-41. 

Fleming  (W.  L.).  “Tungsten.”  Min.  Ind.,  18,  pp.  687-94. 

Forbels  (David).  Quarterly  report  on  the  progress  of  the  iron  and  steel 
industries  in  foreign  countries.  Jou.  I.  and  S.  I.,  Vol.  2,  1872, 
pp.  255-29  4.  Gives  chemical  analysis  of  Mushet’s  “special  steel” 
or  tungsten  steel. 

Frenzel  (A.  B.).  “Growth  of  the  Rare  Metal  Industry.”  Mg.  Sci.,  65,  pp. 
73-74. 

George  (R.  D.).  “Tungsten  Industry  of  Boulder  County,  Colorado,  in  1 90  8. 
E.  M.  J.,  87,  p.  1055. 

— “Tungsten  Mining  in  Colorado.”  Min.  Ind.,  17,  pp.  827-828. 

“The  Main  Tungsten  Area  of  Boulder  County,  Colorado.”  Proc. 

Colo.  Sci.  Soc.,  Aug.,  1909,  38  pp. 

— “Tungsten  in  Colorado.”  Min.  Ind.,  19,  pp.  662-663. 

“Tungsten  in  Colorado  in  1912.”  E.  M.  J.,  95,  pp.  186-187. 

Greenawalt  (W.  E.).  “Tungsten  Deposits  of  Boulder  County,  Colo.”  Cor- 
nell Civ.  Eng.,  Jan.,  1912. 

Guillet  (Leon).  Aciers  au  tungstene.  Rev.  met.,  Vol.  1,  1904,  pp.  263-283. 

Constitution  et  properties  des  aciers  au  tungstene.  Comp. 

Rend.,  t,  139,  Sept.  1904,  pp.  519-521. 

Recherches  sur  les  aciers  au  tungstene.  Genie  civil,  t,  45,  1904, 

pp.  7,.  27. 

Hadfield  (R.  A.).  “Alloys  of  Iron  and  Tungsten.”  Jou.  I.  and  S.  I.,  1903, 
pt.  2,  pp.  14-118.  Presents  bibliography  of  tungsten  and  tungsten 
steels  dating  from  1590. 

Hess  (F.  L.).  Tungsten.  Min.  Res.,  1908,  pp.  726-730. 

„ — , Tungsten,  Min,  Bes.,  1909,  pp,  577-581, 


114 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


Tungsten.  Min.  Res.,  1910,  pp.  733-743. 

Tungsten.  Min.  Res.,  1911,  pp.  941-948. 

Tungsten.  Min.  Res*.,  1912,  pp.  987-1001. 

Tungsten.  Min.  Res.,  1913,  pp.  353-361. 

— Tungsten.  Min.  Res.,  1914,  pp.  937-942. 

Hess  (F.  L. ) and  Schaller  (Waldemar  T.).  “Colorado  Ferberite  and  the 
Wolframite  Series.”  Bull.  U.  S.  G.  S.,  583. 

Hibbard  (Henry  D.).  “Manufacture  and  Uses  of  Alloy  Steels.”  U.  S.  Bur. 
of  Mines,  Bull.  100,  1915,  pp.  16-19,  58. 

Hills  (Victor  G. ).  “Tungsten  Mining  and  Milling.”  Colo.  Sci.  Soc.  Proc., 
vol.  9,  1909,  pp.  135-153. 

Howe  (H.  M.).  “Iron,  Steel  and  Other  Alloys,”  1906,  p.  324. 

Hutchin  (H.  W.)  and  Tonks  (F.  J.).  “The  Determination  of  Tungstic  Acid 
in  Low-Grade  Wolfram  Ores.”  Trans.  I.  M.  M.,  May  13,  1909, 
11  PP. 

JardineJ  (Robert.).  Valves  of  tungsten  steel.  Autocar,  vol.  33,  July  18, 
1914,  pp.  127-129. 

Knecht  and  Hibbert  (E.).  Proc.  Chem.  Soc.,  1909,  No.  360. 

Lee  (Harry  A.).  “Tungsten  Ores  in  Colorado.”  E.  M.  J.,  71,  1900,  p.  466. 

Lindgren  (Waldemar.).  Some  Gold  and  Tungsten  Deposits  of  Boulder 
County,  Ec.  Geol.,  2,  1907,  pp.  453-463. 

Mars  (G.).  Magnetstahl  und  permanenter  Magnetismus.  Stahl  und  Eisen, 
Bd.  29,  1909,  pp.  1673,  1769. 

Die  Specialstahle;  ihre  Geschichte,  Eigenschaften,  Behandlung 

und  Herstellung.  Stuttgart,  1912. 

Ohly  (J.).  “Tungsten.”  Mg.  Rept.,  vol.  44,  1901,  pp.  491-492. 

“Rare  Metals  and  Minerals.”  Ores  and  Metals,  vol.  9,  No.  10, 

1900,  pp.  8-10. 

Paddock  (Carl  H.).  “Tungsten  Milling  in  Boulder  County.”  Mg.  Sci., 
62,  pp.  172-174. 

Palmer  (L.  A.).  “Tungsten  in  Boulder  County,  Colorado.”  E.  M.  .T.,  96, 
pp..  99-105. 

Parmelee  (H.  C.).  “The  Problems  of  Tungsten  Concentration.”  Met.  and 
Chem.  Eng.,  vol.  9,  1911,  pp.  341-342. 

“The  Problems  of  Tungsten  Concentration.”  Canadian  Min. 

Jou.,  vol.  32,  1911,  p.  458. 

Prosser  (Warren  C.).  “Tungsten  in  San  Juan  Co.”  E.  M.  J.,  90,  p.  320. 

Swinden  (Thomas).  Carbon-Tungsten  Steels.  Jou.  I.  and  S.  I.,  pt.  1,  1907, 
pp.  291-327. 

The  Constitution  of  Carbon-Tungsten  Steels.  Jou.  I.  and  S.  I., 

1909,  pt.  2,  pp.  223-256. 

Thomas  (Kirby).  “Mining  in  Colorado,  1907.”  Mg.  World,  28,  p.  164. 

Van  Wagenen  (H.  R.).  “Tungsten  in  Colorado.”  Quart.  Colo.  Sch.  Mines, 
Apr.,  1909,  36  pp. 

Walker  (T.  L.).  “Tungsten,  its  Us*es  and  Geological  Occurrences.”  Mg. 
World,  31,  1909,  pp.  547-548. 

Wood  (Henry  E.).  “Notes  on  the  Magnetic  Separation  of  Tungsten  Min- 
erals.” Colo.  Sci.  Soc.,  vol.  9,  1908-1911,  pp.  154-158. 

Ziegler  (Victor).  “Analysis  of  Tungsten,”  J,  S.  C,  I.,  9,  p.  216, 


MAIN  TUNGSTEN  AREA  OF  BOULDER  COUNTY. 


115 


ANONYMOUS  ARTICLES. 

“Occurrence  and  Utilization  of  Tungsten  Ores,  Part  II.”  Bull. 
Imperial  Inst.,  vol.  VII,  No.  3,  1909,  10  pp. 

“New  Application  for  Tungsten  and  Molybdenum.”  Jou.  Ind. 
and  Eng.  Chem.,  Dec.  1911,  and  Jan.  1912. 

“Tungsten  Mining  in  Colorado.”  E.  M.  J.,  90,  1910,  p.  1058. 
“The  Tungsten  Industry.”  E.  M.  J.,  93,  p.  39. 

“Tungsten  in  Colorado.”  Mg.  and  Eng.  Rev.,  Sept.  5,  1913, 
p.  480. 

“Tungsten.”  Mg.  and  Eng.  World,  36,  1912,  p.  756,  p.  1292. 
“Tungsten.”  Min.  Ind.,  20,  pp.  724-31. 

“Tungsten.”  Min.  Ind.,  21,  pp.  842-51. 

“Boulder  Tungsten  Production  Company.”  Min.  Amer.,  Feb. 

19,  1916. 

“Good  Times  for  Tungsten  Mills.”  Min.  Amer.,  Jan.  29,  1916. 
“Preparation  of  Tungstic  Metals.”  Mg.  and  Sci.  Press,  Jan.  22, 

1916,  p.  134. 

“Concentration  of  Tungsten  Ore.”  Mg.  and  Sci.  Press,  Jan. 

29,  19T6,  p.  166. 


INDEX, 


117 


INDEX 


A 

Acknowledgments  14 

Adams  claim,  reference  to 55 

Adularia  99 

Alaska,  occurrence  of  scheelite  in 47 

Alluvial  deposits  35 

Alloys  104 

Analyses  of  ferberite  from  Gordon  Gulch,  Boulder  Falls,  etc 43 

Analyses  of  ferro-tungsten 92 

Analyses  of  Nederland  ferberite 42 

concentrates  43 

tungsten  minerals  from  other  parts  of  state 43 

Analyses  of  tungsten  steels 94 

Andesites  24,  25 

Arapahoe  glacier,  reference  to 35 

Arapahoe  peak,  reference  to _ 19 

Argentina,  occurrence  of  tungsten  in 58 

Arizona,  tungsten  in 51,  54 

Atolia  Mining  Co.,  method  of  concentrating 8 4 

Assay.  (See  also  Analyses.) 

Australia,  West,  occurrence  of  tungsten  in 57 

South,  occurrence  of  tungsten  in 57 

Australian  method  of  concentrating 84 

Australasia,  occurrence  of  tungsten  in 56 

Austria,  occurrence  of  tungsten  in 58 

B 

Bald  Mountain,  andesites  of 24,  25 

Barker  Ranch,  analysis  of  ore  from 42 

Basalts  31,  32,  33 

Beaver  Creek,  structural  features  of 19 

pyroxene  andesite  dikes  of 25 

alluvial  deposits  on 35 

ores  from 67 

Becket  Process  100 

Beddick  Mine,  reference  to 23,  62,  74,  99 

Big  Colorado  Mine,  reference  to . 55 

Black  Hills,  occurrence  of  wolframite  and  hubnerite  in 48 

Boulder  County  Mine,  discovery  of 13 

reference  to 23 

Boulder  Falls,  analyses  of  ore  from 4 3 

reference  to > 82 

Boyd  Mill,  reference  to  79 

Brazil,  occurrence  of  tungsten  in 59 

British  Columbia,  occurrence  of  tungsten  in 59 


118 


INDEX, 


C 

California,  tungsten  deposits  in 51,  54 

Calcite  99 

Canada,  occurrence  of  tungsten  in 59 

Cardinal,  reference  to 14,  7 6 

Cariboo  Mine,  discovery  of 13 

Cariboo  District,  B.  C.,  scheelite  in 47 

Cement  Creek  Mine,  analyses  of  hubnerite  from 4 4 

Chaffee  County,  scheelite  from 13 

Clarasdorf  mill,  method  of  concentration 7 6,  83 

Climate  and  Vegetation  15 

Clyde  Mine,  analyses  of  ferberite  from 42 

reference  to 61,  75 

Colorado,  hubnerite  found  in 48 

tungsten  deposits  in 53 

Colorado  Tungsten  Corporation  mill,  method  of  concentration 83 

Concentration  of  tungsten  ores 7 6-85,  99,  100 

Conger  Mine,  reference  to 42,  62,  7 4,  99 

Conger,  Sam  P.,  reference  to 13 

Connecticut,  occurrence  of  tungsten  ores  in 47,  54 

Cornish  tungsten  ore  dressing 84 

D 

Dacite  27 

Dawn  of  Day  Mine,  reference  to 55 

Diabase  30 

Dikes  23 

Drainage  15 

Dry  Gulch  Mine,  reference  to 55 

Duralium  104 

E 

Economic  geology 37 

Eldora  Mountain,  monzonite  on 23 

Elmettie  vein,  hubnerite  in 98 

Elsie  Mine,  reference  to 42,  62,  67,  69 

Empire-Victoria  vein,  reference  to 56 

England,  occurrence  of  tungsten  in 57 

Europe,  occurrence  of  tungsten  in 57 

Extension  of  the  Area 96 

P 

Felsite  26 

Ferberite,  concentration  of 80 

description  of 41,  99 

identification  of 44 

market  for 97 

mode  of  occurrence 48 

Ferro-tungsten  92 

Fink,  Dr.  C.  G. — cited 103 


INDEX.  119 

Fluorite  __75,  99 

France,  occurrence  of  tungsten  in 58 


Free  Gold 

G 

Galena  

Garnets  

Germany,  occurrence  of  tungsten  in 

Gilpin  County,  reference  to 

tungsten  in  

Glacial  deposits 

Gneiss,  occurrence  of 

origin  of 

structural  features  of 

Gneissoid  granite.  (See  Granite.) 

Goldschmidt  Process 

Gordon  Gulch  part  of  Tungsten  Area,  analyses  of  ore  from 

milling  of  ores  from 

government  specifications  of 

Granite  and  gneissoid  granite,  fine  grained 

character  of 

Grayback  Mine,  reference  to 

H 

Hal  Harlow  Mine,  reference  to 

Hamlinite  (?)  

Hess  and  Schaller,  cited 

Home  Run  Mine,  ores  from 

Hubnerite,  description  of 

in  San  Juan  

mode  of  occurrence 

I 

Idaho,  occurrence  of  tungsten  in 

India,  occurrence  of  tungsten  in 

Intrusive  rocks  

Italy,  occurrence  of  tungsten  in 

J 


Japan,  occurrence  of  tungsten  in 97 

Johnnie  Ward  Mine,  reference  to 43 

Jones,  Morris,  reference  to 13 

Ii 

Lamprophyre  31 

Last  Chance  Mine,  Analysis  of  ore,  etc * 42,  62 

Latite  . 27 

Latite  porphyry 28 

Lehigh  Tungsten  Mining  Co.,  reference  to 76 

Limburgite  3 4 

Little  Dora  vein,  reference  to 5 b 

J^one  Tree  Mine,  ore  from 74 


43 

99 

99 

72 

37 

13 

48,  98 

52 

58,  96,  97 

23 

5 8 


__  75 

18 
58 
85 

14,  96 

34 
18 
19 

19 

100 

43 

82 

101 

20 
17 
69 


120 


INDEX. 


M 

Magnetite  75 

Magnolia,  reference  to 1 4,  20,  42,  75,  7*> 

Maine,  occurrence  of  tungsten  in 54 

Mammoth  Mine,  reference  to 67 

Manchester  Lake,  tungsten  analysis  from 4 2 

Map,  Tungsten  Area,  Boulder  County 60 

occurrences  in  United  States 50 

Maps,  Tungsten  Area in  pocket 

Metallurgy  100 

Mills,  concentration  7 6 

Minerals  resembling  scheelite,  table  of 40 

Minerals 67-7  6 

Mining  76 

Minnesota  claim,  reference  to 55 

Missouri,  occurrence  of  tungsten  in 53 

Molybdenite  7 5 

Montana,  occurrence  of  tungsten  ores  in 47,  52 

N 

Natalie  Mine,  reference  to 4 4,  56 

Nederland,  stages  of  ore-deposition  in  district 63 

Nederland-Beaver  Creek,  analysis  of  ferberite  from 42 

country  rock  61 

stages  of  ore  deposition 63 

trend  of  veins 62 

type  of  ore 68 

Nevada,  tungsten  in 52,  54 

New  Mexico,  occurrence  of  tungsten  in 47,  53 

New  South  Wales,  tungsten  in 47,  57 

New  Zealand,  occurrence  of  tungsten  in 57 

North  Carolina,  occurrence  of  tungsten  in 53 

North  Star  Mine,  analysis  of  hubnerite  from 44,  56 

occurrence  of  hubnerite  in 48,  56 

Nova  Scotia,  occurrence  of  tungsten  in 59,  97 

O 

Ontario,  occurrence  of  tungsten  in 47,  59 

Oregon  Mine,  reference  to 62 

Ores  67 

Ouray  County,  hubnerite  from__ 44,  55 

P 

Pactolus,  reference  to 36 

Pegmatite  20-22 

Phoenixville,  referenc  e to  1 4 

Portugal,  occurrence  of  tungsten  in 57,  97 

Primos  Mining  and  Milling  Company — 76,  7 9 

milling  methods 82 

Production — . — ,.-59,  86 


INDEX. 


121 


Properties  of  the  metal,  physical  and  chemical 
Pyroxenite  


Q 

Quebec,  occurrence  of  tungsten  in 

Queensland,  occurrence  of  tungsten  in 

R 

Rogers  Tract,  reference  to  

Rollinsville,  latite  near  

reference  to  

Russia,  occurrence  of  tungsten  in 


S 

San  Juan,  tungsten  occurrences  in 

Sardinia,  occurrence  of  tungsten  in 

Scheelite,  description  of 

in  Chaffee  and  Summit  Counties 

in  Tungsten  Area 

minerals  resembling  

mode  of  occurrence 

Siam,  occurrence  of  tungsten  in 

Siberia,  occurrence  of  tungsten  in 

Soda-rhyolite-porphyry  

South  Africa,  occurrence  of  tungsten  in__ 
South  America,  occurrence  of  tungsten  in 
South  Dakota,  occurrence  of  tungsten  in- 

Spain,  occurence  of  tungsten  in 

Stellite  

Sugarloaf  Mountain 

Sultan  Mountain,  tungsten  on 

Summit  County,  scheelite  in 

Sunshine  claim,  reference  to 

Surface  deposits 


T 

Tasmania,  occurrence  of  tungsten  in- 

Texas,  occurrence  of  tungsten  in 

Tom  Moore  Lode,  reference  tp 

Topography  

Townlot  Mine,  reference  to 

Tungstates  : 

Tungsten  alloys 

Area,  extension  of 

future  of  

location  of 

outline  map  of 

bronze  

compounds  

concentrates  from  San  Juan 

tests  of 


103,  104 


— 59 

48,  56 


62,  72 

28 

.14,  33 

— 58 


13,  55 

58 

38,  97,  98 

13 

75 

40 

47,  98 

58 

58 

30 

58 

58 


47,  58 

104 

14,  24,  27 

43,  55 

13 

55 

34 


57 

53 

55 

15 

62,  68,  99 

91 

.91-95,  104 

85 

85 

14 

60 

91 

88-95 

13 

81 


122 


INDEX. 


localities,  foreign 56-59 

in  United  States 49-56 

in  United  States,  map  of 50 

minerals,  description  of 37-45 

metallic,  uses,  etc 87-88 

metallurgy  of 87 

ores,  analyses 42-4  4 

Tungsten  ores,  associated  minerals 75-7  6 

chemical  treatment 82 

concentration  . 76-85 

foreign  production  59 

important  deposits  in  United  States 54-56 

magnetic  separation  82 

modes  of  occurrence,  examples 46-49 

production  of 59,  86,  105 

sale  of  85 

Tungsten  steel,  analyses  of 93 

government  specifications  of  101 

manufacture  95 

production  of 101 

uses  of 94,  101,  102 

Tungsten,  tests  for 45 

uses  of  103 

veins  61-66 

Tungstic  oxide 90 

Tungstic  ochre,  see  tungstite. 

Tungstite  98 

U 

Uses  of  tungsten 101 

Utah,  occurrence  of  tungsten  in 5 2 

V 

Vegetation  15 

Veins  61-7  6 

Virginia,  occurrence  of  tungsten  in 53 

W 

Waltemeyer,  T.  S.,  reference  to 13 

Wanamaker,  W.  H.,  reference  to 13 

Ward,  Johnnie  Ward  Mine,  analysis  of  ore  from 43 

Washington,  occurrence  of  tungsten  in 51 

Wheelmen,  reference  to 62 

Wolf  Tongue  mill,  reference  to 7 6,  78 

Wolframite,  in  the  San  Juan 13 

description  of  37 

mode  of  occurrence 48,  97 

Wood,  H.  E.,  cited 82 

Wyoming,  occurrence  of  tungsten  in 52 

Y 

Yukon,  occurrence  of  tungsten  in 59 


rr  r , r 
i_  JJyA 

I t * 4 \ • ; 

t-  - ■ + 


1 «•/  ? 1 + '■  . 4-  4-  : K . -*-  4 1,  1 

■V  + 4+. 


4*+ 

i J - -i~  - 


+ ijl- , -r  j.  T , +. t 

^AV-hX* 


tr^-r-Tt 


+&+.irH  ‘ 

V+,  'v 


+-  4 + :".'  ■'  L-  + +■  -T 

tVV* r-4.^  r-'4 


f.+  -i-  • -i . - , t t -t 

iSfKl&ILx  .~r:"  ' 


ejvteup 


fTX 


iini 


COLORADO  GEOLOGICAL  SURVEY. 
R.  D.  GEORGE.  DIRECTOR 


FIRST  REPORT.  1908 


eEOBCE'  HBBCiOB 


9^ 


Uo 


-< 


p 

UJ 


O 

u 


ii  LIQ.ifi  ?A  T-S 


COLORADO  GEOLOGICAL  SURVEY.  1916. 


LEGEND 

RECENT 

ETapI 

Alluvium 

RECENT  fc  PLIOCENE 


Moraines 

METAMORPHIC 


|AAqriAN 
ieiS6  and  Scl 


Granite,  qneissoid 


Granite,  qnelssoid, 
fine-qrained. 

(Of  igneous  oriqin) 


DIKES 

i x»  i 

Oacite 


r^n 

Latite 


Latite  Porphyry 


i 

Mica  Andesite 


I — I 

Hornblende  Andesite 


^4^1 
Glossy  Hornblende 
Andesite 

Pyroxene  Andesite 


I S.  I 

Diabase 


I 

Lamprophyre 


Basalt 

Basalt  Porphyry 


l~-b~b  I 

Hornblende  Basalt 

VJ^L 1 

Pyroxenlte 

Limburqite 

X 

Mine 

X 

Prospect 


iiwiuFpsrrv 


